In the development of the rice endosperm, the cell division period, in other words. the period of increase in cell number, ceased on the 9th day after anthesis. Hence, during the 9th day to around the 30th day, the development in size of endosperm tissue should be attained through the enlargement of individual cells. And even in the period prior to the 9th day, the cell enlargement had already been proceeded in the inner portion of the tissue. Length along the top-basal axis of the endosperm tissue reached a maximum on the 6th day, and width (or dorso-ventral diameter) and thickness (or lateral diameter) of the tissue in the middle portion reached a maximum on the 15th and about 30th days, respectively. Every cell situated at any portion of the tissue showed no increase in size in a direction along the top-basal axis. Therefore, development of the whole tissue along the top-basal axis was attained only by the increase in the number of cells through the cell division. This can be understood well from the result of our observation that the enlargement of the whole tissue along the top-basal axis has reached a maximum on the same day when the cell division in this direction ceased. Cells situated at the portion of dorso-ventral axis showed the elongation along the dorso-ventral axis and thus they became column-shape. Such elongation was found out particularly in the cells in the middle portions of the dorsal and ventral radii. Cell elongation was vigorous during the 5th to 10th day, particularly during the 5th to 7th day, and ceased on the 15th day. Because of the several cells on dorsal side elongated more vigorously than those on the ventral side, and because of the fact that the elongation of the former continued up to the 15th day against to the continuation up to the 12th day of the latter, the dorsal radius become longer than the ventral radius, and the 'central point' of the tissue moved gradually toward the ventral side. Cells that situated in the portion along the lateral diameter and those in the intermediate areas between lateral and dorso-ventral diameters grew and formed the flat-polygonal or fan-shape. Cell enlargement of these areas had proceeded rapidly until the 15th day, but thereafter, a slight growth has been continued partially until around the 30th day. Cells which around the central point showed no increase in any direction. The growth habit and the resulted arrangement and the shape of the cells became symmetrical on both sides of the dorso -ventral axis of the tissue.

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Extending over the 6th to 8th day after anthesis, ripening rice caryopses were collected every two hours. Samples thus collected were fixed with FAA, and then cross sections obtained from the middle portion of the endosperm were stained with Delafield's Haematoxylin. Cell division occurred mainly in the early morning (from 2 a. m. to 8 a. m., accounting for 50-72% of the all samples), and after passing through the rest stage in the day-time (from 10a. m. to 4 p. m. ), it reoccurred in the evening. It was observed that from evening to midnight, the time for cell division and resting stage were repeated alternately (Tables 1 and 2). The periodicity of cell division had connection with the day-night rhythm, while it was thought that the pattern of the division cycles might differ according to age of the tissue. Average time required per cell division was 45-55 minutes. Resting time in early morning was very short, while that in the day-time was very long. It became evident that the section of the cell division was not confined to the outermost cell layer of the endosperm. Namely, 86% of the total cell division was observed in the outermost cell layer of the tissue, and 14% in the 2nd and interior cell layers. Basing on the observations, the process of the tissue formation shown in the Report 1 on this investigation has come to be revised, because in the case of Report 1, the tissue formation process had been deduced from the hypothesis that the cell division occurred only on the outermost layer. In the case of division of the cells found in the interior portion of tissue, the features have been found in that the cells were divided into two caused by the nuclear division which occurred after the enlargement of size of cells has reached twice as large as the surrounding ones.

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On the dorsal side of the endosperm on the 5th day after anthesis, the cells on the outermost and the second layers were smaller in size and stained more deeply with Haematoxylin and Millon's reagent than the cells on other layers. They increased to 3 or 4 layers by their own cell division and then differentiated to the aleuron layers by the 6th-7th day. Cells adjacent to the inside of particular cell layers continued to increase the number of starch cells by the cell division up to the 8th day, and some of them also differentiated additionally to the aleuron cells on the 9th day. On the lateral and ventral sides, the cells on the outermost layer showed a slight particularity, but still continued to make cell division in order to increase the number of starch cells up to the 7th or 8th day, and then differentiated to the aleuron cell layer on the 9th day after the final cell division. The aleuron cell was morphologically completed on around the 15th day. The date for its completion coincided with the date for the completion of the enlargement of the starch cells.

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In case of Japonica paddy rice varieties, the number of aleuron cell layers averaged 4.2 on dorsal side, 1.1, 1.2 on lateral and ventral sides, respectively, and 1.0 on midway portion between lateral and ventral sides. No difference was found in the number of aleuron cell layers among the sample varieties (Table 1), among the varietal groups classified according to grain size (Table 2), and between glutinous and nonglutinous strains (Table 1). In case of Japonica upland rice varieties, the number of aleuron cell layers on dorsal and ventral sides were larger than those of the Japonica paddy varieties (Table 3). In foreign varieties, the number of aleuron cell layers on dorsal side was less than those of Japonica ones. Especially, tested varieties of Indian and Chinese varieties are less than 3 layers (Table 4). The number of aleuron cell layers on the dorsal side of incompletely developed grains was less by about one layer than that of the full-grown grains in the same panicle. Regardless of completely or poorly developed grains, at least one cell layer of aleuron was formed on the lateral and ventral sides (Table 5). In case of early season cultivation in which the ripening stage is shifted to warmer season it showed the effect of increase in the number of aleuron cell layers on the dorsal side, but almost no effect on the leteral and ventral sides. The same tendency was found also in case where the ripening stage of Indica varieties was shifted to warmer season (Table 6).

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Attached roots and detached roots of rice plants were examined for the rates of respiration and nutrient absorption under an aerobic condition, adopting the methods stated in the previous reports. The results obtained may be summarized as follows; 1. There were no marked differences in the rates of respiration and nutrient absorption of attached roots whether they were kept under an aerobic condition or not. 2. When detached roots were exposed to an aerobic coditon, they carried on almost normal respiration being followed by promotion of nutrient uptake, comparing with those exposed to an anaerobid condition. But they took up less amount of nutrients than attached roots in spite of the rate of respiration being rather accelerated. That may be the reason why detached roots were kept under conditions disadvantageous to nutrient absorption, as stated in the previous report. Besides, some othe reason was considered. 3. In case NaN₃ was added to the culture solution, the rates of respiration and nutrient uptake both of attached and detached roots were severely depressed even if they were kept under an aerobic condition. 4. Attached roots showed a strong oxidizing power whether they were kept in an aerated or nonaerated medium. In contrast the oxidizing power of detached roots was decreased markedly when they were kept in a non-aerated medium, although they could reveal an oxidizing power as strong as that of attached roots when kept in an oxygenated medium. The oxidizing power of both kinds of roots which had been grown in the culture solution containing NaN₃ was always depressed whether they were kept in an aereted mediun or not. 5. From the results stated above as well as those reported in the previous papers, it may be concluded that the roots of rice plants can perform almost normal respiration and nutrient absorption even if they are exposed to a poorly oxygenated medium so for as no substances harmful to respiration are present there. Because the rice roots can receive molecular oxygen enough to sustain aerobic respiration from the the tops through the well-developed ventilating system.

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The experiment dealts with the growth and morphology of callus in various varieties of rice belonging to Japonica and Indica types. The result indicates that Te-Tep has the highest growth rate among fifteen varieties used, reaching 3.13 g/5 seeds in fresh weight in 30 days at 30°C (table 2). There was observed the friable or compact callus (figs. 1 to 15). Te-Tep grows to the most compact callus, and Konan-senhas the highest growth rate among friable callus. According to an estimation of the diameter of nuclei with 100 cells of each callus, they indicates 6.3μ to 7.5μ wide in average value (table 3). It call be said that the nature of callus, friable or compact, growth rate, and size of the nuclei are independent to the types of variety, Japonica or Indica. It is interesting that the giant nuclei over 11.0μ appeared at a rate of 0.5 per cent of all nuclei observed. 5.5μ to 7.4μ of nuclei were 60.5 per cent. It was also observed that callus initiation and development in solutions of various concentrations of 2, 4-dichlorophenoxyacetic acid were different according to the varieties used, exception for Vialone nano which did not initiate callus at all at 1μM of 2, 4-D (table 1).

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In order to clarify the compensatory translocation of carbohydrates occurring among the culms of paddy rice plant after heading, the panicles or leaf-blades of those culms (e. g., the main culm, all the primary culms, all the secondary and tertiary ones, or the entire culms) were removed at the heading stage, and after ripening of the respective culms, the grains of each panicle were counted by assorting them into three groups; (1) unfertilized grains, (2) incomplete ones, and (3) complete ones (with specific gravity of more than 1.08 each). The grains (1) and (2) are hereinafter referred to as "waste grains". Complete grains (3) were hulled and their 1, 000 kernel weight was taken. Special attention should be directed to that per-hill paddy rice plants used for this experiment consist of the main culm (one), 7 primary culms, 14 secondary ones, and 4 tertiary ones. Our test resuls are summarized as follows; (1) Removing of panicles of some culms within a hill gave a favorable influence on the ripening of remaining untreated culms, resulting in the decrease of their waste grains. In contrast to this, removing of leaf-blades of some culms within a hill gave unfavorable influence on the ripening of the remaning untreated culms, resulting in the increase of waste grains. For instance, the removing of panicles or leaf-blades of all the primary culms gave almost the similar effects not only on the ripening of the main culm and the secondary culms but also on the ripening of the tertiary ones. The number of waste grains decreased by half by removing the panicles of the primary culms, and increased nearly double by removing their leaf-blades. Removing of the panicles or leaf-blades of all the secondary and tertiary culms gave also almost the similar effects on the ripening both of the primary culms and the main culm, and the number of waste grains decreased nearly by half due to removing of the panicles, and increased nearly double due to removing of the leaf-blades, Moreover, the same effect wass also brought on the upper primary culms not having their own secondary and tertiary ones. (2) The ripening of those culms of which leaf-blades were removed was also affected by other culms of which leaf-blades were not removed. In case where the leaf-blades of the main culm alone were removed, its waste grains decreased to less than the half, as compared with those of the main culm in the plot in which leaf-blades of all the hill were removed. In case where the leaf-blades of all the primary culms were cut, thier waste grains decreased nearly by half, comparing with those of the primary culms in the plot in which leaf-blades of all the hill were removed. And in case where the leaf-blades of all the secondary and tertiary culms were removed, their waste grains were larger in number than those of the above two cases, but the significant differences were found evidently between the number of the waste grains of the culms of which leaf-blades of all the hill were removed and that of the waste grains of the culms of which the leaf-blades of the secondary and tertiary culms were removed. The varation of such differences can be ascribed to the ratio between the number of the culms of which leaf-blades were removed and that of the culms of which leaf-blades were not removed. (3) In case where the so-called waste grains showed increase or decrease in the number as given above, the number of unfertilized grains roughly showed proportionate changes with at of incomplete grains. However, when it showed particularly great increase in the number of waste grains, it showed a relatively great increase in the number of unfertilized grains. (4) No great differnces were found in 1, 000 kernel weights of complete brown rice, except for a few cases where leaf-blades of too many culms were removed. [the rest omitted]

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The laboratory test was conducted to provide the fundamental information about the most efficient method of rough rice drying. 1) Hulls have a function to prevent kernels from rapid dehydration, acordingly, during rough rice drying, dehydration in hulls is easy and rapid but that in kernels is hard and slow. When dehydration in kernels is enforced by immoderate drying, cracks are formed in kernels as the time elapses. It is, therefore, thought that the alternate repetition of rapid drying of hulls by relatively high temperature for a short time and transfusing of moisture from wet kernels to dried hulls during tempering is the most efficient method of rough rice drying. As shown in fig. 1, after drying by temperature of 65°C for 15 minutes, moisture content in hulls dropped from 17.7% (wet basis) to 11.0%, whereas, moisture content in kernels dropped only from 21.7% to 20.9%, and during tempering moisture in kernels removed into dried hulls and moisture content in them became 20.0% and 14.0% respectively. (The moisture content of 14% in hulls is fairly lower than the moisture conten of hulls equilibrated under natural condition (*), on account of hysteresis.) Thus, the kernels were dried from an initial moisture content of 21.7% to a final moisture content of 14.3% during 6 passes in a total drying time of 63 minutes. 2) The amount of moisture removed in each drying has influences to efficiency of drying and to crack formation in kernels, and the critical amount of dehydration in each drying that does not form crack in kernels is varied by the initial moisture content in rice. In the moist kernel, above about 25% in moisture content (dry basis), crack scarcely occures by drying on account of softness of kernel tissue. Consequently, as shown in fig. 2, the critical amount of safety-dehydration is raised from 1.0% to 1.5% (dry basis) according as the initial moisture content rises from 25% to 27%. When the inital moisture content is less than 25%, the lower the initial moisture content becoms, the more easily crack is formed, therefore, the critical amount of safety-dehydration drops from 0.9% to 0.6%. The same relation between the critical amount of dehydration and the initial moisture content is observed in unhulled rice. But, the curve of the critical amount of dehydration in unhulled rice has more steep inclination than that in hulled rice, because the amount of dehydration in unhulled rice is a total of amounts of dehydration in hull and kernel, and the amounts of dehydration in hull becomes larger as moisture content in unhulled rice rises higher. When drying is not so rapid as this experiment, the critical amounts of dehydration are more or less higher than those in these figures. 3) The time of tempering required to equilibrate the moisture between hulls and kernels is effected by the amount of dehydration and also by ambient temperature. In this experiment, it is about 2 hours under the condition that the amount of dehydration is in the range of the critical dehydration in fig. 2 and ambient temperature is about 40°C as shown in fig. 4. (fig. 5.) The equilibration of moisture among the portions in kernel is also accomplished in 2 hours. 4) This drying method has no harmful influence on rice in regard to germination and cooking characteristics. (table 1) Whereas, when ambient temperature rises 66°C by drying temperature of 76°C, germination is slightly injured and the total solids content in residual liquid becomes appearently less. 5) This principle on rough rice drying will be applicable not only to articficial drying but also to sunn drying in tropics and will be avairable to preventing the occurence of "sun checking".

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In Setonaikai districts premature blossoming is frequently observed in tobacco plants transplanted at the stage of 11th or 12th leaf. In order to escape from the occurrence of this phenomenon, seedlings with less number of leaves than 11 or 12 are used to be transplanted especially in the case of the flue-cured variety, Hicks I. -2. For the clarification of the causes of this phenomenon, studies were made for three years on the relationship of seedling age and transplanting period to morphological characteristics of plants at flowering stage. Results obtained were as follows; 1). Seedlings with 9 to 12 leaves of Hicks I. -2. variety were used. With increased age of seedlings used for transplanting, the subsequent time required for flowering decreased, accompanying with plant height and total leaf number at flowering stage. Plants transplanted at 11th or 12th leaf stage showed the typical type of premature blossoming, which had narrow leaves and decreased number of them. 2). The later the transplanting period, the more number of leaves plants bore. But the trends mentioned above were observed as well. 3). Plants transplanted later by keeping the seedlings growing in the seed-bed, not up to 12th leaf stage, bore no less number of leaves than those transplanted immediately at the stage fit for transplanting.

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Two experiments were performed in order to find periodic effects of low and high temperature upon the developmental responses of tobacco seedlings with different ages. The flue-cured variety, Hicks I. -2 was used in both experiments. Seedlings with 8-12 leaves were cultivated for tests in the greenhouse (16-25°C, 14 hrs. photoperiod). In experiment I, they were exposed to low temperature (13°C) for 10, 15, 20 and 25 days under long-day condition. Then they were transferred to the greenhouse maintaind at 20±3°C. Relation between age of seedlings and their vernalization was examined. In experiment II, seedlings were subjected to low temperature (15°C) interrupted by high temperature (30°C) for 3.5 hrs. in daytime under long-day condition. Then devernalization by means of high temperature was investigated. The longer the period of low temperature, the earlier the floral initiation. Seedlings with more number of leaves responded rapidly to low temperature and the difference in the response among seedlings with different ages was remarkable when they were treated for shorter days. High temperature given for a short time prolonged the floral initiation of tobacco seedlings. Difference in the developmental responses among 9th to 12th leaf seedlings was remarkable in plants encountered with the treatment of high-temperature-interruption after a low-temperature-treatment for 15 days.

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Effects of temperature in seed-bed and field upon premature blossoming of tobacco plants were examined. The flue-cured variety, Hicks I-2 was used. In expriment 1, 9-12th leaf seedlings were grown under two different seed-bed conditions. The one was the commercial seed-bed covered with vinyl-film, the other a seed-bed set in a greenhouse. Minimum temperature was lower in the former by ca. 8°C as compared with that in the latter. These seedlings grown under different conditions were transplanted to the fiield and the same ones were transferred to the phytotron maintained at 20°C under natural day-length condition no April 8th in 1962. Plants cultivated in the fiield showed the same trends reported in the previous paper (I). The more advanced in age the seedling transplanted in the field, the earlier the flowering date, the lower the plant height and moreover the less number of leaves. But with plants transplanted from the greenhouse to the field, these trends were less observable. On the other hand, plants produced greater number of leaves in the phytotron than those in the field. And with plants cultivated in the phytotron, difference was not observed in total leaf number among seedlings with different ages, accompanying with no effect of the seed-bed condition upon the developmental responses of tobacco seedlings. These facts suggested that it was not day-length but temperature, especially in the field, that caused differences in total leaf number. In experiment II developmental responses of tobacco seedlings were examined in 1962 and 1964. Seedlings of 8-12th leaf stage cultivated in the commercial seed-bed were transplanted to the field on April 12th in 1962 and on April 13th in 1964 respectively. The same results as reported in the previous paper (I) were obtained in 1962. But in 1964, leaves were produced at higher rate and no difference in time for flower-bud formation among seedlings with different ages was observed. Consequently, plants bore greater number of leaves in contrast to that in 1962, and total leaf number increased with increased age of seedlings used for transplanting. The reason why these phenomena occured was able to be explained by comparing the changing pattern of diural mean temperature in both years. That is to say, in 1964 diural mean temperature was higher throughout the growing season as compared with that in 1962. But diural temperature rose gradually in 1962, and did not so in 1964. The development of tobacco seedlings was greatly influenced by temperature and the difference in total leaf number among seedlings with different ages arose chiefly from the changing pattern of diural temperature, which was confirmed in several experiments carried out by many procedures.

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Radioactive CO₂ gas feedings in an assimilation chamber were conducted on Ladino clover plants in different stages of regrowth after cutting to reveal the translocation of ¹⁴C-assimilates in the plant body. To prepare for the simultaneous treatment, the plants grown in pots were cut on different dates so that they were on their 18th, 15th, 12th, 9th, 6th, and 3rd day of regrowth and immediately after cutting. All plants were fed ¹⁴CO₂ for 2 hours in an assimilation chamber at the same time. ¹⁴CO₂ feeding experiments werd repeated three times, and 1st experiment plant were harvested immediately after ¹⁴CO₂ feeding, while in the 2nd and the 3rd experiment the plants were harvested 2 days and 5 days after ¹⁴CO₂ feeding, respectively. Sample were prepared with Van-Slyke-Folch's wet-oxydation apparatus and radioactivity of various parts of the plants were counted by gas-flow type counter. With the same assimilation chamber and design of experiment, another feeding experiment of ¹⁴CO₂ was conducted. The plants were harvested 2 days after feeding and the radio-autographs were taken. The results of these experiments led us to the following findings. 1) Of the plant immediately after cutting, the young leaves which had not yet opend assimilated ¹⁴CO₂ though in small amounts, but no translocation to other parts of plant was seen (Fig. 3 Fig. 6-A). 2) Of the plant 3 days of regrowth, the leaves assimilated actively, and the assimilates were seen being exported to the opening leaves at the growing points. Export to the reserve organs such as stolons and roots was observed but very slightly (Fig. 3 Fig. 6-B). 3) Of the plant 6 days after cutting, the laeves assimilated very actively the actvity reaching the highest level. The transport to the reserve organs started at this time, the radioactivity in the stolons and roots were increasing (Fig. 3). 4) The most rapid increase in radioactivity in the stolons and roots was seen in 6 (lays to 9 days after cutting (Fig. 3 Fig. 6-D). With the increase of leaf area the ratio exporting ¹⁴C-assimilates to the reserve organs increased (Fig. 5).

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Macro-and microscopic observations were carried out to clear the causes for lowering of fertilization due to the application of gibberellin in rice plants, using a slightly late variety "Sachikaze". Gibberellin was applied at the stage of young panicle differentiation mixed with the culture solution at 100 ppm. Though remarkable increase, about 40 percent, of spikelets in number was brought about by the treatment, simultaneously about 62 percent of the total spikelets has resulted in sterility in the mature panicles. As shown in fig. 1, tables 2 and 3, the sterile spikelets due to the so-called "white hulls" took place at the basal portion of the lower primary branches and the other sterile, particularly the perfectly sterile ones, spikelets were observed on the middle and upper primary branches. With the immature panicles of the gibberellin plot, collected about two weeks after the heading date when the gibberellin induced morphogenetic abnormalities in spikelets were clearly discernible, receiving no disturbance due to the withering, and yet the conditions of fertilization could be judged by the degree of ovary development, the morphogenetically abnormal spikelets and the "white hulls" mounted up to about 60 percent of the total number of spikelets, being almost the same value as the percentage of sterile spikelets in the mature panicles mentioned above. Distributive pattern of the abnormal spikelets in the immature panicles was also very similar to that of sterile ones in the mature panicles. Not only the "white hulls" but also nearly all spikelets which had any morphogenetic abnormality in their floral organs, such as, glumes, stamens and pistils had resulted in the complete sterility or parthenocarpy as shown in figs. 2-11. From the above results, a major cause for the lowering of fertilization due to the gibberellin treatment was considered to be the morphogenetie abnormality which had been induced by gibberellin in the process of spikelet formation, though the immediate relationship between them was not clear in this study. The histological observations were shown in figs. 12-15. As seen in them, the development of the inner tissues of carpel, such as, epidermis, crushed parenchyma, about two layers of cross cells and a layer of tube cells, was almost normal, but that of ovule, especially nucellus was abnormal. No alleuron layer nor starch tissue as well as embryo have generated in the embryo sac. On the parthenocarpic caryopses seen in the gibberellin plot, it was indicated that they resembled closely to those which were reported to be caused by auxins with castrated rice flowers and were usually found in rice plants grown under an unfavourable low temperature, both in morphological and histological characteristics. The relation between auxins and gibberellin on the revelation of parthenocarpic caryopses, and that between these hormonic substances and the physiological background of spikelet morphogenesis under an unfavourable low temperature were discussed to some extent.

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For investigation of heading habits of so-called photoperiod-sensitive rice varietis under long-day conditions, the two following experiments were conducted in 1966. (1) Ten sensitive japonica varieties including Zuiho, one of the most sensitive varieties, were cultured in pots under 24-hr daylength in greenhouse. (2) The variety Norin No. 29 grown under long-day (24-hr) condition was treated with different number of photo-inductive cycles (8-hr) at different stages. In the first experiment, though the days to heading or the shape of ears were different with varieties, all the ten varieties could come into ears within 114-200 days. So it may be concluded that photo-sensitive japonica rice varieties can shift from vegetative phase to reproductive phase under 24-hr daylength condition. In the second experiment, the authors found the three limiting photo-cycles specific for each age, the plant of higher age needs less cycles. According to cycles given more or less than the limiting one for some age, the heading habit of the plant is distinguished as follows: (A) When treated with enough cycles for the age, the plant will come into ears in fewer days and with normal shape. (B) With less cycles than that for (A), premature death or mal-formation of ears is expected. (C) Cycles more insufficient for the age result in delayed emergence of the normal ears. (D) Cycles under the lower-most limiting ones produce almost little of the stimulus and let the plant come into ears almost at the same time as the untreated plants. The authors clarified in the first experiment that short-day condition isn't essential for heading of japonica varieties, but with reference to the fact of (B), it seems that the plant given some photo-inductive cycles requires short-day condition for some while after floral differentiation also, and that short-day condition given after floral differentiation accelerates ear-emergence. In case of tillers, their heading is independent of primary culms; that is, in relation to the time of tiller-sprouting and the time of short-day, treatment, some of four above-mentioned aspects of heading can be expected.

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The mesophyll structure of rice leaves inserted at different levels of the shoot were observed. The individual cells of the mesophyll are tabular in shape, having several lateral protuberances or arm-like processes. In transverse section, these look like folds inwardly directed from the cell wall. These cells are so-called the arm-palisade cells. The protuberances are columnar or hemispheric in shape and their diameter (r) is nearly the same as the cell thickness (T). On the adaxial surface of the leaf, the protuberances are conspicuously elongated at right angles to the leaf surface. The upper leaves have thicker mesophyll than the lower leaves. The ribs and furrows are more developed on the adaxial than the abaxial surface of the leaf. The ratio of the adaxial mesophyll surface area to the leaf area (MS/LA) increases in the upper leaves. The number of protuberances in a mesophyll cell increases from the lower to the upper leaves. The cell thickness is smaller in the upper leaves than that in the lower. Therefore, the ratio of the cell surface to the cell volume (S/V) is increased in the upper leaves. The total cell surface per unit leaf area is enlarged in the upper leaves, as a result of increase in the number of cells.

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Rice plants were grown under the shade of natural daylitght during the 13th and 14th leaves were expanded. The mesophyll structure of those leaves were observed and following results were obtained. 1) The mesophyll thickness of the shaded leaf is thinner than that of the unshaded leaf, as a result of diminution of the individual cell volume and the cell number per unit leaf area. 2) Adaxial surface of the shaded leaf is flatter than that of the unshaded leaf, as a result of reduction of the differences in mesophyll thickness between the ribs and furrows and elongation of the distance between the vascular bundles. Therefore, the ratio of the adaxial mesophyll surface area to the leaf area (MS/LA) is reduced in the shaded leaf. 3) The total cell surface area per unit leaf area is reduced in the shaded leaf, as a result of diminution of the cell number and the individual cell surface. 4) The effect of shading on the mesophyll structure of the 13th leaf is not always the same as that of the 14th leaf. In the 13th leaf, the number of cells per unit leaf area and the distance between the vascular bundles are not affected by shading, but the protuberance number per cell and the protuberance length at the adaxial surface are reduced in the shaded leaf. From the observations of this study, it will be suggested that the mesophyll thickness, the ratio of the adaxial mesophyll surface area to the leaf area and the total cell surface area per unit leaf area may be anatomical characteristics, lowering the photosythetic activity of rice leaves developing in the shade.

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In order to investigate the desirable growth phase of direct snwn rice plant, the experiment was undertaken to make clear the effects of nitrogen deficiency at the early growth stage on the growth phase of the plant by water culture method. The results obtained are as follows: 1. According to the period of nitrogen deficiency at the early growth stage of the plant becomes loner, the rate of leaf appearance was delavyed prominently, and the number of leaves on main stem was redubed, on the other hand, after having been supplied with nitrogen the rate of leaf appearance was more accelerated than before. Therefore, in cace the nitrogen deficient period was not too long, the plant was able to recover the number of lenves on the main stem. 2. So far as nitrogen nutrition is concerned, the coleoptile, the 1st leaf (next leaf of coleoptile) and the 2nd leaf blade grew up normally with nitrogen nutrition in the seed itself, and their growrths were not effected by nitrogen nutrition in nutrient solution, but the growth of the 2nd leaf sheath, the 3rd leaf (sheath and blade) and that follows were controlled remakably by nitrogen in nutrient solution. And in this experiment, the plant age which was able to grow up nomally with nitrogen in the seed was limited to the 2nd leaf stage of the young plant. 3. As the period of nitrogen deficiency at the early growth stage becomes longer, the weight of dry matter in top of the young plants was reduced remarkably, but after the plant have been supplied with nitrogen, the rate of increase of dry matter weight became larger. The dry natter weight of roots also showed the same tendency with that of the top, but the differences among the separate plots were not so remarkable as that of the top. 4. As the nitrogen deficiency period at the early growth stage becomes longer, the plant height became gradually shorter, but after having been supplied with nitrogen, the elongation of plant height was more accelerated than before, therefore, the plant height delayed in the early growth stage has recovered, and except -N plot, after the heading time the differences among the separate plots were not observed. 5. As the nitrogen deficiency period became longer, the number of stems decreased and the -N plot bore no tiller. 6. As to the heading time, differences among the separate plots were not oaserved, and the -N plot showed marked delay. 7. When the nitrogen deficiency period was short, there was practically no influence on the culm length, but when the period became too long, it acted to shorten the culm length. 8. The plots of nitrogen-deficiency-treatment generally bore longer ears than the control plot. 9. As the nitrogen deficiency period became longer, except the -N plot, the number of ears, weight of ears (yield), weight of straw and weight of roots (air-dried) decreased. However, the (weight of ear)/(weight of straw) ratio and the percentage of effective culms increased. As shown shown above, the nitrogen-deficiency-treatment at the early growth stage in dieect-sown rice plants gave a marked influence on the growing habit of young rice plants. However, after administering nitrogen, the rate of growth was increased and as long as the nitrogen deficiency period was not too long, the delayed of growth during the treatment peried could be recovered. Not only that but rather a reasonable degree of nitrogen-deficiency-treatment at the early growth period prevented the occurrence of over-growth which is one of the greatest defects of direct sown rice plants, and made it possible to raise the (weight ofe ars)/(weight of straw) ratio and the percentage of effective culms. It might be said that using such plants denser planting will be possible leading to an increased number of ears per unit area, and subsequently, to an increased yield.

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Chlorotriazines, simazine, propazine and atrazine; methoxy substituted triazines, simeton, prometon and atraton; and methylmercapto substituted triazines, simetryne, prometryne and ametryne were used in this experiment in order to make clear their phytotoxicity for rice plant and barnyardgrass at the germinating stage. The results obtained were as follows: 1. There were apparent differences among these three substitutes in the toxicity both for rice plant and for barnyardgrass. Namely the toxicity for rice plant, listed in the increasing order, was methylmercapto-, methoxy-, and chloro-triazines. In the case of barnyardgrass, too, this tendency was the same, but the differences among the substituted radicals were slightly smaller than in rice plant. 2. The selectivity in toxicity, which is higher for barnyardgrass than for rice plant, was markedly different according to the substituted radicals: The methylmercapto triazines were extremely selective, the methoxy triazines slightly, and the chloro triazines little. 3. From the above-stated results, it was found that the methylmercapto triazines, simetryne, prometryne and ametryne were the most suitable herbicides for weed control in paddy fields.

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As was reported in the previous paper, it was found that the methylmercapto triazines, simetryne, prometryne and ametryne were most suitable for weed control in paddy fields. In this experiment, the influence of temperature on the phytotoxicity of these herbicides for rice plant and barnyardgrass was examined both by the treatment of foliage under flooded conditions at the seedling stage and by the treatment of underground parts at the germinating stage at 16, 23 and 30°C, respectively. The results obtained were as follows: 1. The influence of temperature on the toxicity for rice plant and barnyardgrass was markedly different according to the herbicides in each of both treatments. Namely the effect of temperature on the phytotoxicity of simetryne was slight, but in the case of prometryne and ametryne it was severe. The latter two herbicides were much more toxic at 30°C than 16 or 23°C, especially for rice plant. 2. In both treatments, the selectivity of simetryne in toxicity, which was stronger for barnyardgrass than for rice plant, was very high with little influence of temperature. On the other hand the selectivity of prometryne decreased at higher temperature, and ametryne had extremely low selectivity at 30°C than at lower temperatures. 3. The influence of temperature on the toxicity for rice plant and barnyardgrass and on the selectivity between both plants was higher in the treatment of underground parts at the germinating stage than in the foliage treatment under flooded conditions at the seedling stage. 4. Judging from the above-stated results, simetryne was found to be more widely suited for weed control in paddy fields in view of the effect of temperature.

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The following chemicals among 27 ones tested were more or less effective for breaking seed-dormancy or killing dormant seeds in the soaking treatment in which dormant barnyardgrass seeds were immersed in water solution with 100 to 1, 000 ppm of each chemical for one or more days at a constant temperature from 25°C to 35°C. NIP (2, 4-dichlorophenyl-4-nitrophenyl ether), emulsifiable liquid; CNP (2, 4, 6-trichlorophenyl-4-nitrophenyl ether), emulsifiable liquid; KK-60 (2, 4'-dinitro-4-chlorodiphenylether), emulsifiable liquid; AM. (allyl-2-methyl-4-chlorophenoxy acetate), emulsifiable liquid; DNBP (4, 6-dinitro-o-sec-buthylphenol) amine salt, solution; 1-thiocyanato-2, 3-dibromopropane (U-1), emulsifiable liquid; 1, 3-dithiocyanato-2-bromopropane (U-2), emulsifiable liquid; 1-isothiocyanato-2-bromopropene (U-3), emulsifiiable liquid; 1-thiocyanato-2-bromopropene (U-4), emulsitiable liquid; α-(2, 4-dichlorophenoxy)-acetonitrile (X-1), emulsifiable liquid; α-(2, 4-dichlorophenoxy)-propionitrile (X-2), emulsiftable liquid; PCP water-soluble powder, DBN wettable powder, C1-IPC emulsifiable liquid, MCP sodium salt solution, AM wettable powder and NIP granule were not effective under the condition of this experimental treatment.

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Six chemicals, which were found effective in the previous report, were examined in various conditions of the soaking treatment in order to make clear the factors influencing their activity. The results were as follows; 1. Soaking of the domant seeds in 500 ppm emulsion of NIP for 5 days or in 1, 000 ppm for 3 days at 30°C respectively broke the dormancy sufficiently. More breaking was observed at the higher concentration of the chemical or higher temperature, with the longer soaking period, or in cases in which degree of dormancy of tested-seeds was weaker. When the activity of the chemical was too high, most of the seeds lost viability. 2. Emulsion of 1-thiocyanato-2, 3-dibromopropane (U-1), 1, 3-dithiocyanato-2-bromopropane (U-2), 1-isothiocyanato-2-bromopropene (U-3) and 1-thiocyanato-2-bromopopene (U-4) showed remarkable activity in breaking dormancy. The seeds lost viability when the activity of these chemicals was too high. The order of activity of these chemicals was as follows; U-1≤U-2《U-4≒U-3. In order to break the dormancy almost completely, barnyardrass seeds had to be soaked for 2 to 4 days in 500 ppm solution of U-1 or U-2, and for 2 days in 100 ppm or for 4 days in 50 ppm of U-3 or U-4 at 30°C, respectively. 3. The dormant seeds were killed by a soaking treatment in 1, 000 ppm solution of DNBP (amine salt) for 3 days at 30°C. The activity was markedly decreased at the temperature below 20°C. 4. The solvents themselves used for the formulation of these chemicals showed some activity in breaking dormancy, though, in general, it was a limited one. The activity of chemicals, however, varied according to the formulating method of chemicals such as kind of solvent used. The formulating method, therefore, was assumed to have such effects on the activity of the chemicals possibly through affecting their permeability into barnyardgrass seeds. 5. In the screening of effective chemicals for breaking the seed-dormancy or killing the seed by means of the soaking treatment, degree of dormancy of tested seeds and formulating method of the chemicals as well as temperature and duration of the treatment were considered to be important factors. Even in testing chemicals which aim to break the seed-dormancy, it was may be pointed out that not only the number of awakened seeds but also that of killed seeds should be counted.

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Effectiveness of four chemicals, NIP (2, 4-dichlorophenyl-4-nitrophenyl ether), 1-isothio-cyanato-2-bromopropene (U-3), 1-thiocyanato-2-bromopropene (U-4) and DNBP (4, 6-dinitro-o-sec-buthylphenol), which showed high activity in the soaking treatment, was examined under the presence of soil using petri-dishes or 1/5000 a pots. Three methods were used for the treatment: spraying of the chemical solution to the seeds placed on the surface of water-drained soil, applying of the chemical solution to the seeds placed on the surface of water-submerged soil, and incorporating of the chemical solution to the upper layer of water-drained soil with the seeds. The results obtained were as follows: 1. Effectiveness of each chemical varied according to the method of treatment. NTP, U-3 and U-4 were more effective in the following cases: in case the effect of breaking dormancy by the method of treatment itself was higher, or in case the concentration of chemical solution in contact with the seeds was higher. This fact was especially remakable in NIP. DNBP was most effective when it is sprayed directly to the seeds. 2. The effectiveness in these treatments in contact with soil, in general, was markedly less than in the soaking treatment. Therefore, it was assumed that the treatment given under the presence of soil might have several factors decreasing the activity such as the adsorption and decomposition by soil or the vaporization of chemicals. 3. Generally speaking, such dosages as above 400 g/a in NIP, 200 g/a in U-3 or U-4 and 400 g/a in DNBP were required for full activity. 4. In order to establish the technique for breaking the dormancy or for destroying the germinability of dormant barnyardgrass seeds in soil by chemicals, it is important to find out not only chemicals with higher activity but also methods or factors which will improve the permeability of such chemicals into the seeds.

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