In this studies we observed on opaque kernel, especially green opaque kernels. The results are summarized as follows: 1) Opaque kernels are classiffied in several types according to its shapesas green opaque kernel (type 6, type 7-1, type 7-2, ), white opaque kernel, small translucent green kernel, and monstrous kernel. Tissue and outlook of green opaque kernel are shown in Figure 1 to Figure 12. Type 6 and type 7 showing green opaque kernel, have immature parts (starch-less tissue) in endosperm as in Figure 4, 6, 8, 10, 12. 2) Developmental process of kernels are classified into 6 types showing in Table 1. According to Table 1, early growth of opaque kernels are suppressed by the competition of superior kernels. And in the late ripening stage at 17 days after flowering, opaque kernels grow comparatively rapid. 3) From the incressing curve of 1000 kernels weight of inferior spikelet, we observed the competition of growth of kernel among inferior spikelet and superior spikelet as in Figure 9. 4) Protein content of opaque kernels are always richer than ripened kernels. 5) If we could promote growth of opaque kernel in late stage of ripening, some of these might be grown to ripennd kernel in harvesting time, then we consider that above results show its possibility.

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This paper deals with carbon-dioxide environment in cover-culture of tobacco plant. Results obtained are as follows: 1. In the closed type covering (with polyethylene film), carbon-dioxide concentration increased at night, decreased at day. Daily minimum carbon-dioxide concentration in that covering decreased with the number of days after transplanting, and it became as low as the natural air concentration at the 12th (transplanted on May 23rd) after and at the 9th (transplanted on April 5th). On the other hand, carbon-dioxide concentration in the opened type covering (with melamin resin coated paper) was epual to the natural air at day or night. 2. Carbon-dioxide concentration in the closed type covering with paper was influenced by moisture of the paper, i. e. in case of the covered paper wetted with rain or dew, carbondioxide concentration changed in the same course with that in the covering with polyethylen film, but it remained almost constant all day, when the paper was dried. 3. The maximum photosynthetic rate of the tobacco plant in the covering occurred some time between 7 : 00 and 9 : 00 a. m. 4. Dry matter production of tobacco plant in the covering with paper (closed type) was better than the covering with polyetylene film (closed type). It may be one of the reason that carbon-dioxide concentration keeped high in daytime.

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[in Japanese]

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Growing rice seedling for 30 days under each condition of all possible combinations of air-temperatures (16°C·21°C·31°C and 36°C) and water-temperatures (16°C·21°C·31°C and 36°C) and transplanting them again under each condition of all the combinations of air- and water-temperatures as mentioned above, the authors examined the relation of rooting ability of the seedlings to growing conditions in the seedling period and the characteristics of seedlings. The results obtained might be summarized as follows. 1. The number of roots newly emerged, the length of roots newly elongated, the number of leaves newly died and the numbes of leaves newly emerged on the main stem after transplanting were investigated, as indexes of rooting ability, on the 10th day after transplanting. 2. As a result of examining the relation between rooting ability and growing conditions in the seedling period, the number of roots newly emerged after transplanting appeared to be mainly influenced by water-temperature not by air-temperature in the seedling period, and it showed the largest value on the seedling grown under the water-temperature of 31°C. On the other hand, the largest value in length of roots newly elongated was found on the seedlings grown under low water-temperatures such as 16°C or 21°C. The number of leaves newly died after transplanting was much less on the seedlings grown under low water-temperatures than on those grown under high water-temperatures, and the number of leaves newly emerged on the main stem was larger on the seedlings grown under low air- and water-temperatures than on those grown under any other air- and water-temperature. 3. As a result of examining the relation between rooting ability and temperature conditions during the rooting period, rooting ability appeared to be mainly affected by water-temperature not by air-temperature on any index of rooting ability, so the most desirable value was obtained at 31°C and the most undesirable value was found at 16°C of water-temperature on any index of rooting ability. 4. The seedlings, which showed the most desirable values on all the four indexes of rooting ability and also showed actually highest rooting ability under the most conditions during the rooting period, appeared to be raised under the combined condition of relatively low air- and water-temperature such as air-temperature 21°C and water-temperature 16°C, air-temperature 21°C and water-temperature 21°C, and air-temperature 31°C and water-temperature 16°C in the seedling period. 5. The seedlings, which showed the most undesirable values on all the four indexes of rooting ability and also showed actually lowest rooting ability under the most conditions during the rooting period, appeared to be raised under the highest water-temperature, i. e. 36°C, in the seedling period. 6. The characteristics of seedlings which showed high rooting ability seemed to be small in plant age, in number of roots and in ratio of the weight of leaf-blades to the weight of leaf-sheaths, but large in content of chlorophyll in leaves.

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Growing rice seedlings under the various conditions of all possible combinations of air-temperatures (16°C·21°C·31°C and 36°C) and water-temperatures (16°C·21°C·31°C and 36°C) and furthermore subjecting them to a shading treatment (20% shading) or a heavy fertilizing treatment (5 times dosage), the authors examined the combined effects of these factors on the characteristics of seedlings. 1) The plant height, top dry-matter, root dry matter, T·R ratio and the ratio of top dry-matter to plant height are more strongly influenced by the water-temperature than by air-temperature, except in the case of air-temperature 16°C, and the highest or near highest value of each character above mentioned is obtained under the condition of air-temperature 31°C combined with water-temperature 31°C. 2) The plant age in leaves advances slower at air-temperature 16°C than other-temperatures, and there are little differences in the progress of plant age among the treatments of air-temperature 21°C, 31°C and 36°C, while it advances progressively faster as the water-temperature goes up. 3) The percentage of decayed roots is strongly influenced by the water-temperature, not by the air-temperature, and it becomes higher without exception as the water-temperature goes up. This fact suggests the importance of controlling water-temperature in raising healthy seedlings. 4) As the air-temperature goes up, nitrogen content as well as carbohydrate content progressively decreased. This fact also suggests that the low air-temperature serves for raising good and healthy seedlings. 5) The shading treatment has a detrimental effect on every character investigated (except plant height) in all conditions, except at the air-temperature 16°C and the water-temperature 16°C. This fact suggests the importance of exposing seedlings to sunlight as much as possible for raising and healthy seedlings. 6) Heavy fertilization has a good effect on the most characters investigated, in particular on the ratio of top dry-matter to plant height. This fact also suggests the importance of studying heavy fertilization in seedling period.

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Growing rice plants in solution culture under a community condition and stopping nitrogen supply for 20 days at different stages of growth, the authors studied the effects of nitrogen depletion at various growth stages on the growth and yield of rice. As previously reported, no supply of nitrogen during the critical growth period in which the plant type after heading was predetermined made the rice plant decrease the number of spikelets per unit area, length of lower three internodes and upper three leaf-blades, but increase the amount of carbohydrates in straw at heading stage, and as a result of it, favoured ripening and prevented the plant from lodging. The three treatments which stopped nitrogen supply for 20 days from 59, 49 and 42 days before heading respectively were high in grain yield on account of the percentage of ripened grains being much increased. This high percentage of ripened grains in the present experiment could firstly be ascribed to decreasing the number of spikelets per unit area and increasing the amount of carbohydrates in straw at heading stage, and secondarily to controlling excessive growth, improving plant type and preventing the plant from lodging. The length of upper three leaf-blades was shortest in the treatment which stopped nitrogen supply during the period from 42 days to 20 days before heading, and the length of lower three internodes of rice plants was shortest in the treatment which stopped nitrogen supply from 49 days to 31 days before heading. In this experiment, however, the effect of improvement in plant type and light-utilizing efficiency on the rate of carbon assimilation, the increase in dry-matter after heading and the grain yield were hardly recognized, probably because the leaf-area-indexes in the experiment were not so high enough as the plant type could affect the photosynthetic efficiency. So far as the experiment was concerned, the amount of photosynthetic production after heading was mainly governed by the amount of nitrogen in leaf-blades at heading time as well as that of nitrogen supply after heading, and scarcely affected by the leaf-area-indexes, leaf-length and light-utilizing efficiency. (The plant type would play an important role in increasing photosynthetic production after heading when the leaf-area-index would be higher than 6.4.) The results in the present experiment are considerably different from those of pot experiments in same kind so far conducted, probably because the light condition after heading is so good in pot experiment that the grain yield is simply increased by only increasing the number of spikelets per unit area.

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In the previous paper (No. 73) the authors pointed out that the plant type after heading has a close relation to the percentage of ripened grains under luxurious growth conditions and, therefore, the study of plant types is quite necessary for maximizing the yield of rice. In the other papers (No. 58 and 66) they also clarified that the top-dressing of nitrogen at a definite growth stage makes the plant elongate a definite leaf-blade, leaf-sheath and internode, while the restriction of nitrogen supply shortens each of them. On the basis of these facts, the authors considered that under the rice cultivation in which only basical fertilizers are applied and not top-dressed at all, if the varieties differing in the maturation period are transplanted on an identical date, the effectiveness of nitrogenous fertilizers will also appear on an identical date, as a result of it, the longest leaf-blade will be found on upper nodes in short-term varieties, while it will be found on lower nodes in long-term varieties. For examining this point, the authors investigated nine varieties differing in the maturation period for three seasons, confirming the following facts. The longest leaf-blade is found on the second node from above in very short-term varieties, on the third node in short-term and medium-term varieties, and on the fourth node or fifth node in long-term varieties. In other words, the longest leaf-blade appears on the lower node as the variety becomes longer in the maturation period. As to the length of leaf-sheaths, the upper most one is always longest in most cases. But the second longest oneis found on upper nodes in short-term varieties and on lower nodes in long-term varieties as in case of leaf-blades. Since the growth of a leaf-sheath is synchronized with that of the immediate upper leaf-blade, the second longestleaf-sheath is found on the third node from above in very shortterm varieties, on the fourth node in short-and medium-term varieties, and on the fifth or sixth node in long-term varieties.

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Subjecting two leaf-aged rice seedlings to the conditions of all possible combinations of day-water-temperatures (16°C·21°C·31°C and 36°C) with night-water-temperatures (16°C·21°C·31°C and 36°C) for 26 days, the authors examined temperature effects on the growth of seedlings. (The daytime is taken from 6 a. m. to 6 p. m. and the nighttime from 6 p. m. to 6 a. m.) The results may be summarized as follows. 1) Increased plant height during daytime is greater than that during nighttime when day-water-temperature is higher than night-water-temperature, but it turns reversely when day-water-temperature is lower than night-water-temperature, and it is almost equal to that during night-time when day-water-temperature is equal to night-water-temperature, which suggests that the growth of rice seedlings is mainly influenced by the temperature factor and not by the light factor at all. Furthermore, the optimum combination of day- and night-water-temperature for increasing plant height during daytime is observed to be the combination of day-water-temperature 31°C with night-water-temperature 21°C, while for increasing plant height during nighttime to be the combination of day-water-temperature 21°C with night-water-temperature 31°C. The fact suggests that the optimum combination of day- and night-water-temperature for increasing plant height during daytime is different from that for increasing plant height during nighttime. 2) Response of plant height and root length to the various combinations of day- and night-water-temperatures are in the same pattern as each other. Both plant height and root length increase progressively faster as day-water-temperature as well as night-water-temperature rise up to 31°C, but they increase slowly at 36°C, When the average water-temperature of day and night is identical, the increase of plant height or root length is always slightly greater in the case of day-water-temperature being higher than night-water-temperature than in the case of the reverse. 3) The plant age expressed by leaf number of the main stem respenses differently from the other characters. It is affected only by the average water-temperature of day and night, not being affected by the daily range of water-temperature during day and night, and it advances progressively faster as the average water-temperature rises up to 36°C. 4) The number of tillers increases with the rise of average water-temperature during day and night and with the increase of daily range of water-temperature during day and night. The tillers which branch out from lower nodes fail to develop as the average water-temperature during day and night rises and as the daily range of water-temperature during day and night decreases. 5) The weight of dry-matter increases without exception with the rise of average water-temperature during day and night up to 31°C, but it responses to the water-temperatures differently from the above-mentioned way when the average water-temperature goes up above 31°C. In case of the average water-temperature during day and night being above 31°C, if water-temperature is higher during daytime than during nighttime, the dry-matter is always heavier, but if water-temperature is lower during daytime than during nighttime, the dry-matter is much lighter than that at day-water-temperature 31°C combined with night-water-temperature 31°C. In other words, ill-effects of high night-water-temperatuer on the increase of dry-matter can be clearly recognized in the case of average water-temperature being above 31°C. Furthermore, in case of the average water-temperature of day and night being identical, the dry-matter in the condition of day-water-temperature being lower than night-water-temperature is always much lighter than that in the condition of day-water-temperature being higher than night-water-temperature. [the rest omitted]

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After classifying the rice plants which grown under several cultural conditions in last few years into the several groups according to the number of spikelets per unit area, the authors studied the percentage of ripened grains from an analytical investigation of the number of spikelets per unit area, obtaining the following results. 1. When the number of spikelets per unit area was extremely small, no definite relation was found between the percentage of ripened grains and any component of the number of spikelets per unit area (i.e. the number of panicles per unit area, that of spikelets per panicle and that of primary and secondary rachis-branches per panicle). 2. The percentage of ripened grains showed a tendency to decrease progressively with an increase in the number of spikelets per unit area, spikelets per panicle and secondary rachis-branches per panicle, while it seemed to increase with an increase in the number of panicles per unit area. 3. When the number of spikelets per unit area was extremely large, the percentage of ripened grains was positively correlated with the number of panicles per unit area and negatively correlated with the number of spikelets per panicle as well as the number of secondary rachis-branches. 4. In case of the number of spikelets per unit area being large, the fact that the percentage of ripened grains decreased with an increase of the number of spikelets per panicle could be explained from the fact that the number of spikelets per panicle increased with a decrease of the amount of carbohydrates stored in sheaths and culms before heading and that of photosynthetic products after heading.

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To examine the factors in different moisture content of rice according to rice grain texture, the studies were undertaken to clarify the relationship between the moisture content measured by the several drying methods at different temperatures and the grain texture of several varieties. The results are summarized as follows. 1. Globe of fat, crystal of protein and a part of starch granule contained in hulled rice were collapsed owing to the drying at temperature of I05°C (hereinafter referred to as "I05°C drying"), and it was recognized that the marginal tissue of rice grain containing fat and protein was scorched by the I05°C drying, and that the components came to be collapsed by the I35°C drying, and at that high temperature the scorch of the marginal tisste of endosperm was also recognized. But, it was recognized that these were not collapsed or scorched when dried by the vacuum oven method (referred to as "V. O. D" : 1/1000 mmHg, 97±2°C). Therefore, if the moisture content of rice when dried at lower temperature than that by V. O. D is regarded as free moisture content, the moisture content of rice by the V. O. D could be regarded as "all free moisture content", and the difference between the moisture content by I35°C drying and that by V. O. D could be regarded as "bound moisture". 2. The moisture content of hulled rice by the I05°C drying is higher than that by the V. O. D, and the moisture content of the internal polished rice (containing about 30% polished rice), is lower than that by the V. O. D. Therefore, it is recognized that under I05°C drying condition the bound moisture is contained in the moisture content of hulled rice. So that, all free moisture content must be measured under the V. O. D condition. 3. Generelly, atmospheric humidity has direct effect upon the moisture content by 70°C drying, but not affect on free or bound moisture content under the drying condition at higher temperatures than 70°C. 4. The free moisture content is usually higher in starch-cell tissue, in coarser tissue, in unripened kernel and in soft verieties of rice. Than in bran tissue, in compact tissue, in fully rippened kernel and in hard varieties respectively. The bound content is usually higher in bran and aleuron layer in the marginal tissue of rice grain, than in starch-cell tissue, and higher in fully ripened rice kernel, and semi-soft varieties of rice (somewhat harder than soft varieties of rice).

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Increase in size of the starch granules began to precede from the central portion of endosperm tissue and reached the maximum size (39μ in major diameter) by the 15th day after anthesis falling on around 10 days after begining date of the granule formation. According as a portion of the endosperm tissue was on the more outside, the begining date of the granule formation was delayed more, and the increase in size of the starch granules proceeded at a slower pace. Accordingly, starch granules found in the exterior cell layers were always smaller in size than those found in the interior ones. And the starch granules in the outermost cell layer facing the aleuron layer were delayed most. Their final size was as small as 6μ in major diameter on about the 35th day after anthesis, i.e., on around 25 days after begining of starch granule formation. Average size of the whole starch granules showed increase at the most remarkably rapid pace during the period from 10th to 18th day after anthesis, and continued to show an increase until the 35th day to the extent of 23×19μ, thus completing the increase in size. It was generally found that there was little or no significant difference in size of the starch granules contained in each cell. And that it seemed that there was no any appreciably great difference in the number of starch granules in each cell, irrespective of remarkably great differences in size of cells. Size of starch granules of the sample variety "Yoneshiro" (japonica) was generally larger than that of starch granules of such sample varieties as "T136" and "Mushakudanti" (indica). We inferred the following types of routes of translocation of the material substances composing of starch granules into the endosperm tissue. At the very early stage, direct translocation of substances into endosperm from surrounding nucellus (route a) might be fairly noticeable, besides the supply of substances from the vascular bundle on the outside of dorsal side (conducting strand). In and after milk-ripe stage, route (a) had no longer been noticed. Instead, the route (b) translocation "conducting strand→nucellar epidermis→surface cell layer of endosperm (aleuron layer)→starch cell layers" seemed to have probably played the important role in translocation. In and after dough-ripe stage, it seemed that translocation route has come to be increasingly confined to the route (c) translocation "conducting strand→nucellar projection→dorsal side of endosperm". In spite of the fact that the pathway of starch materials in the endorperm cell was becoming increasingly narrower due to the growing size in starch granules after dough-ripe stage, a considerably large amount of materials have been translocated through the endosperm tissue. From this fact, it is suggested that the starch materials have been translocated not only by the simple physical stream in the cell, but also with a help from a certain "carrier" which pocesses enzymatic or chemical activities.

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It is well known phenomenon that abnormal hypertrophy of tapetum takes place in rice plants encountered with an unfavourable low temperature. In a previous paper we have discribed the phenomenon of abnormal hypertrophy of tapetum might be an incidence controlled by the level of endogenous auxin during the anther development. This experiment was carried out with the purpose to prove if exogenously supplied auxins can induce the same abnomral hypertrophy of tapetum as that caused by the low temperature. Naphthaleneacetic acid (NAA) and 2, 4-dichlorophenoxyacetic acid (2, 4-D) were used at concentrations of 0.1, 1.0 and 10.0 ppm. The young spikes at the period of first and second constructions of micrspores were floated on the solution of chemicals for 24 hr at room temperature. Then the anthers were fixed in FAA and prepared for histological observations by means of the usual paraffin method sectioning about 10μ in thickness. Various types of tapetal abnormalities as shown in figs. 2∼17 were observed in the anthers treated with auxins, especially in the plots of the higher concentrations. Thus it became clear that the auxins used obviously induce or promote the same tapetal hypertrophy as that caused by the low temperature. These results seem to support the concept previously reported by the writers that appearance of the tapetal hypertrophy under the low temperature might have a close relationship with the endogenous level of auxin during the anther development. The interaction between auxins and RNA in connection with the abnormal development of tapetum was discussed quoting Dr. Shibuya's experimental result that the tapetal abnormality was induced by application with uridine-monophosphate or triphosphate plus glucose-1-phosphate.

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Preliminary studies were carried out to examine the effects of iron on the appearance of morphogenetical abnormalities due to an unfavourable low temperature in rice spikelets. 10 ppm of iron was supplied in the nutrient solution by way of Fe·EDTA (chelating agent with iron), Ferric Citrate and Ferric Chloride, the control concentration of iron being 1 ppm supplied with Ferric Citrate. Also a plot of Na·EDTA was provided in order to clarify the influence of EDTA containing the same amount of iron as the control. It was found that iron, given as Fe·EDTA, showed a remarkable inhibitory effect on the appearance of morphogenetical abnormalities and they were totally or partially eliminated in presence of Fe·EDTA even under an unfavourable low temperature, though the other plots did not give any desirable effect. Some discussions were tried on the relationships between the auxin action and iron from the hormonal aspects, but this paper did not offer any reason why the inhibitory effect was brought about by the Fe·EDTA, leaving the detail physiological interpretation to the future investigations. Ineffectiveness of Ferric Citrate and Ferric Chloride was considered to be attributed to the difficulties in the uptake or absorption of them by plants.

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Comparative effects of gibberellin and auxins-naphthaleneacetic acid (NAA) and 2, 4-dichlor-ophenoxyacetic acid (2, 4-D)-on the induction of parthenocarpic caryopses were studied using three rice varieties, "Fujisaka No. 5", "Sachikaze" and "Tokaiasahi". The chemicals were sprayed on young flowers which were emasculated just before anthesis and the flowers cut two weeks after treatment were used for observations. NAA and 2, 4-D, especially the latter, produce the parthenocarpic caryopses efficiently but unexpectedly at any concentration of 0.1, 1.0, 10.0 and 50.0 ppm of gibberellin failed to promote the growth of the ovary wall parthenocarpically. Above results indicate that in rice plants the effective growth substances to induce the parthenocarpy may be auxins and not gibberellins when they are applied at the stage of anthesis. Several workers have reported on the effectiveness of gibberellins in stimulating parthenocarpy in various plants. The reason why gibberellin does not display the same effect on the rice plants may be an interesting problem to be resolved in the near future. Furthermore, it was found that even in the control plots (emasculated and sprayed with distilled water) the parthenocarpic caryopses were observed frequently in two varieties used, especially in "Tokaiasahi", the latest maturing variety of all. This indicates that in rice plants there is possibility to induce the parthenocarpy without the pollination process and that in some varieties there seems to be enough endogenous auxin in the ovary at the stage of anthesis to promote the growth of the ovary wall by itself. The result previously reported by the writer that frequent parthenocarpic caryopses can be induced by gibberellin treated at the stage of young panicle primordium differentiation should be considered to be resulted not with the direct but the auxin-mediated effect of gibberellin during the pistillate organ development with or without pollination. Also, on the prevailing phenomenon of parthenocarpy in rice plants caused by an unfavourable low temperature, the endogenous auxin should be considered to be an important factor stimulating the ovary wall growth with or without pollination process.

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Several lines of investigation have been carried on the formation of lysigenous lacunae of rice plant roots. The results obtained so far, however, do not agree with each other on the mechanism of formatlon and physiological significance of the lacunae. It was reported by many investigators that the development of the lacunae of rice plant roots growing under anaerobic soil conditions was remarkable as compared with that of aerobic soil conditions. It was assumed that oxygen needed for root respiration would be supplied mainly by leaves via stems and lysigenous lacunae when the rice plant was kept in anaerobic soil. On the other hand, an investigator asserted that the physiological role of lysigenous lacunae of rice plant roots should be reexamined from that the formation of lysigenous lacunae had relations with the development of lateral roots, that the fomation of lateral roots in the soil of paddy field was generally accelerated when it was in oxidative state and that the development of lacunae, on the contrary, was slowed down when the soil was reductive. In an attempt to throw the light on the differences observed in these works, the histogenesis and the changes in the volume of lacunae and lateral roots were studied in rice seminal roots growing under two kinds of soil conditions in oxidation-reduction potentials. The phenomenon of cortical disintegration may be consisted of two phases, emergence and enlargement. With the exception of roots, 2 days old growing under reductive soil conditions, the emergence of cortical disintegration was always observed with the primordia of lateral roots. In two days roots growing under reductive soil conditions, the emergence of cortical disintegration was found, but the initiation of lateral root primordia was observed nowhere. While the enlargement of cortical disintegration was noticeable more distinctively in the roots growing under oxidative soil conditions (hereinafter referred to as O) than in the roots growing under reductive soil conditions (hereinafter referred to as R) for 4 days after seeding. Though there were little differences in the density of lateral roots and the primordia on the same aged parts (e. c. was 0.9 cm length from root base in O and 0.6 cm in R), for 4 days after seeding O exceeded distinctly R in the volume of lateral roots per centimeter and the growth of lateral roots in length of which the longest lateral roots represented of each region abovementioned. On and after the 4th, R was superior to O in the percentages of lacunae, the volume of lateral roots and the growth of lateral root in length. On the basis of such results, it was assumed that the emergence of cortical disintegration and the initiation of lateral roots have a close relationship with each other in time and position, and the enlargement of cortical disintegration was restricted by the velocity and the volume of the growth of lateral roots. Anyhow, the results of this experiment seem to indicate that whether the development of cortical disintegration will become well in R or O, depends mainly on the growth of lateral root in volume or velocity. A difference, as previously stated, in observations among investigators with refference to the extent of the development of cortical disintegration in R and O may be consolidated by these results.

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The nutritional and hormonal requirements for the growth of callus derived from root-tuber tissue of sweet potato "var. Kokei No. 14" are described in the present investigation. When the tissue disk derived from root-tuber was placed on an agar medium containing White's minerals, 2% sucrose, yeast extract and auxin, a callus formed and developed on the surface of the disk, and in subculture it grew speedily and continuosly on the same medium. The favorable concentration of yeast extract for the formation and growth of callus was 0.3∼0.5%, and when the amount of yeast extract in the medium was lower than 0.2% there was no continuous growth of callus. From the result of partially substituting casamino acid (0.1%) and kinetin (0.01mg/l) for the large amount of yeast extract, it may be suggested that the growth-promoting activity of yeast extract for the callus of sweet potato was fairly attributed to its cytokinin and amino acids. It was also reported that for the formation and growth of callus exogenous auxin is necessary. 2, 4-D (0.1∼1mg/l) as well as NAA (10∼20mg/l) stimulated the callus formation and maintained its growth, but IAA was ineffective in this respect. In rare case, root formation occurred in the callus on the NAA-medium, but there was no sign on the medium containing 2, 4-D. The favorable concentration of sucrose for the formation of callus of the tissue disk was found to be 5%, but in subculture 2% sucrose showed the excellent growth of the callus.

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Two varieties of flue cured tobacco plants (var. Bright Yellow and var. Hicks) were exposed to various high temperatures for 2 hours in daytime for 2 weeks. Plants were grown in the growth room maintained at 18°C in the experiment 1, and in the uncontrolled greenhouse in the experiment 2 during the treatments, respectively. Heat treatments were conducted in each growth chamber at temperatures of 18 (check), 33, 38, 43, 45 and 48°C respectively in the experiment 1, and of 26 (check), 48, 53 and 58°C in the experiment 2. After these treatments plants were transferred to greenhouse and grown to bloom. Total number of leaves and days to flowering increased with increasing temperatures. Plants of var. Hicks showed somewhat similar responses of flowering at the temperatures between 48 and 53°C. There were similar modal curves of the rate of leaf emergence in both varieties during the treatments. The rate increased with temperature up to about 33-38°C and declined at higher temperatures than 38°C. It was obtained that the rate of incresed total number of leaves per unit degree °C (an index of thermal sensitivity) increased with temperature up to about 38°C in var. Hicks and 45°C var. Bright Yellow, then declined at higher temperatures than those in both varieties. Thus, var. Hicks was less sensitive to thermal exposure than that of var. Bright Yellow. Another index of thermal sensitivity expressed on the rate of retarded days to flowering was increased with temperature at any plot of exposures in experiment 2. The area of the largest leaf at flowering stage was reduced with temperature in both varieties, specially, it was seriously decreased at the exposures to higher temperatures over 43°C. Plant height at flowering stage increased with temperature in both varieties, even in the 48°C plot. From this fact, together with the result of leaf area, it was suggested that the effects of high temperatures upon the growth of tobacco plants might be different between each organ of the plant.

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Seedlings of flue cured tobacco were exposed to various high temperatures for short time in daytime, and their subsequent responses were observed. Heat treatments were conducted in each high temperature chamber maintained at 18 (check), 33, 38, 43 and 48°C for 2 hours in the experiment 1. And the temperatures of 26 (check), 48, 53 and 58°C for 3 hours in the experiment 2. Varieties employed were Bright Yellow in the experiment 1 and Hicks in the experiment 2. Plants were exposed to successive 8 treatments in the experiment 1, and similarly 14 treatments in the experiment 2. Then their growth were determined and aliquot of plants in each plot was transferred to greenhouse and grown to bloom. Stem length was increased with temperature, but its tenency was reduced at the temperatures higher than 43°C in the experiment 1, whereas in the experiment 2, it was decreased with temperature higher than 48°C, especially at 58°C it was seriously reduced. Emergence of leaves during treatments was reduced with increasing temperatures in any plot higher than 48°C, especially at 58°C plot. Changes in expansion of leaf area with time was increased most rapidly at the temperature of 33°C and declined at both higher and lower temperatures than this during experiment 1, whereas it was reduced proportionally with increasing temperatures in the experiment 2. There were apparent differences in the areas between upper and lower leaves. The area of upper leaves exposed to 33°C was the largest and reduced proportionally with temperature apart from 33°C, but thore exposed to high temperatures were larger than untreted control. On the contrary, the area of lower leaves exposed to high temperatures was reduced with increasing temperatures than untreated control plants except for 33°C plot. Dry matter of plants rose up to 33°C and then fell with increasing temperatures, but those exposed were larger than untreated plants except for 48°C. Apparent difference was observed in the dry matter distribution between stems and leaves. The portion of stem was increased and that of leaf reduced with temperature during exposures. Dry matter of leaves rose to maximum at 33°C and fell with increasing temperatures in the upper and middle leaves, but those exposed to high temperatures were larger than untreated plants except for 48°C in the middle ones. On the contrary, they were reduced with temperature in the lower leaves. Leaf area of the upper at the flowering stage rose to maximum at 43°C then fell again and that of the middle rose to maximum at 38°C and then fell with increasing temperatures but those exposed were larger than that of untreated plants except for 48°C in the middle leaf. Whereas that of the lower leaf reduced with increasing temperatures except for 33°C during experiment 1. On the other hand, in the experiment 2, leaf area was reduced in the lower leaves and increased in the upper at exposed plants as compared with untreated plants. But as compared with in each exposed plot, the leaf area was reduced by higher temperatures. The largest leaf was relatively in the upper position in the exposed plants as compared with untreated control plants. Serious injury was showed by a single or double exposures to 58°C in the experiment 2.

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Seedlings of flue cured tobacco (var. Bright Yellow) were exposed to high temperature of 43°C for 1, 2 and 3 hours each in successive 14 days in daytime. The area of middle and lower leaves reduced with the durations of exposures, but the area of the upper of exposed plants was larger than that of untreated control. Dry matter of leaves and tops rose up to 2 hours exposure and then fell with the length of exposures. On the contrary, dry weight of stem increased with time of the exposures. The portion occupied by stem increased with time and the exposures in the day, whereas the portion of leaf, vice versa. Dry matter production of middle and lower leaves reduced with the exposure to high temperatures but that of the upper was larger than that of untreated control. Dry weight per unit leaf area of the middle and lower reduced with increasing the exposure except for 1 hour exposure of middle leaf. On the contrary, that of the upper was increased by the exposures to high temperature. Plant height of flowering stage increased with the duration of exposures to high temperature, and leaf area of the largest leaf at flowering stage was reduced by the exposures as compared with that of untreated control. Total number of leaves and days to flowering were increased by the durations of exposures to high temperatures. Rate of leaf emergence was reduced by the increasing exposures, and floral induction was retarded by the durations of exposure to high temperature.

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There is a intimate corelation between the absorption amount of potassium and tuber-yield of sweet potato in wide range. However, it had been vain attempted to increase the dosage of potassium application with ordinary procedure for get a very high yield. Then we carried out various experiments on the application method of potassium. In the investigation of root system of the sweet potato, a interesting fact was found out that the roots occurrenced from the stem were located in a shallow soil layer near of surface, but the roots developed from the tauber were located in deep soil layer. Another fact also recognized that abundantly potassium exist in deep soil layer at high-yield-field of sweet potato. Consequently, mineral nutrients were applicated the both layers, shallow and deep, through the plowing before planting. We got a conclusion as a follows; it is very effective in order to tuber-yield increasing to applicate the potassium in deep soil layer, 30 cm or 40 cm depth, at fertile soil, and it is desirable to applicate with together potassium, nitrogen and phosphorus at arid field.

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