It is well known that application of heavy rate of nitrogen fertilizer to obtain higher yield of rice give a negative effect a cool weather year. For adequate nitrogen application, critical nitrogen cantents in leaf blade at the booting stage in relation to booting sterility were surveyed in the materials which were supplied with nitrogen : basal and top dressing at the spikelet differentiation stage. The curves of nitrogen content in leaf blade at the booting stage-relative value of fertility were drawn by free-hand. Relative value of fertility generally decreased slowly at first, then very rapidly with the increase in nitrogen content. The advance of these processes was similar irrespective of different temperatures, varieties and experimental sites (Figs. 5, 6, and 7). The critical nitrogen contents in leaf blade which were calculated from these curves (content at which fertility attained 90% of fertility in minimum nitrogen content plot) were 3.0∼3.3% in Shiokari and 3.3∼3.6% in Ishikari, respectively.

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The effect of compost application on cool temperature sterility at the booting stage was investigated in the field where water temperatures were precisely controlled (±0.5°C). Compost application showed a protective effect from yield loss caused by cooling treatment at the booting stage in the fields where the yield level at ordinary temperature was higher than 600kg/10a (Fig. 1). This protective effect from yield loss was primarily due to a decrease in sterility (Table 1). Sterility in the compost plots was lower than that in the control plots at the same level of leaf nitrogen content in the range above 3.0% of leaf nitrogen content (Fig. 2). Carbohydrate content of the mixture of leaf sheath and culm was higher in the compost plots than in the control plots, when they were compared on the basis of the same level of leaf nitrogen content (Fig. 3). The fresh weight of root was greater, and the activity of α-naphthylamine oxidation in root was higher in the compost plots than in the control plots (Figs. 4, 5).

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In a previous paper, we have shown that no difference in total dry matter weight per area at harvest was observed between old (ear-weight type) and new (ear-number type) types of cultivars, but that the new types produced less dry matter before heading and more dry matter after heading than the old ones. It was considered that this difference in dry matter increase between both types could affect directly the yield components which were determined at various growth stages. The present investigation was carried out to analyse the chronological changes in the characteristics of grain production in comparison of old types with new types of cultivars. Attempts were also made to compare cultivars in the warmer part of Japan with those in the cooler part (northern area of Japan) which has the reputation of being a high yielding area. Grain yield was higher in the new types than in the old types of cultivars. Grain yield was more closely correlated to the harvest index (r=0.919^***) than to the total dry matter weight (r=0.630^N.S.) (Fig. 1). There was no difference in sink capacity, defined as spikelet weight with the exclusion of grain per area at harvest, between old and new types of cultivars (Table 1). The new types produced more dry matter as compared with their sink capacity, suggesting that their sink capacity is small (Figs. 2 and 3). The enlargement of leaf area which was caused by the increase in sink capacity was more pronounced in rice plants growing in the warmer part than in the cooler part of Japan (Figs. 4 and 5). This phenomenon could be ascribed to two factors, firstly the temperature which is higher in the warmer part of Japan, secondly the fact that the new types in the warmer part had fewer spikelets per ear and a larger increase in ear number per area than those in the cooler part (Figs. 8, 9 and 10). Consequently, the new types had a lower sink/source ratio in the warmer part (Fig. 5). Here, sink/source ratio was defined as the ratio of sink capacity to leaf area at heading. But the old types of cultivars had still a higher sink/source ratio than the new types (Fig. 5). In contrast, in the cooler part of Japan, the sink capacity was adequate. Also, due to the higher number of spikelets per ear in addition to a small leaf area index, the sink/source ratio has tended to increase lately (Figs. 4 and 8). From these results, it appears that the sink capacity of rice plants growing in the warmer part of Japan should be higher to achieve further increase in grain yield. However, the increase in the sink capacity would be very difficult to achieve since new types of cultivers with many and small ears require heavy nitrogen and high planting density. Then, in these types the leaf area becomes readily enlarged, excessive growth would result. Therefore, it would be desirable to breed cultivars with high sink capacity but without excessive growth.

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In general, the new types of cultivars have a shorter culm and more ears than the old types. In a previous paper, it was demonstrated that the new types produced less dry matter before heading due to their short stature. In this paper, we compared the dry matter production of one of the new types of cultivars (Asominori) growing in the warmer part of Japan with that of the improved japonica-indica hybrid cultivar Milyang 23, which was released in Korea in 1975 and is well known for its high yielding capacity. There was no difference in culm length between Asominori and Milyang 23 but Milyang 23 was taller than Asominori in all stages of growth (Table 1). Milyang 23 produced more dry matter than Asominori during the period of growth from ear initiation to harvest (Fig. 1). Leaf area index (LAI) of both cultivars changed similarly in all stages except in the later ripening stage, and crop growth rate (CGR) and net assimilation rate (NAR) were higher in Milyang 23 during the growth period from ear initiation to harvest (Fig. 2 and 3). The values for the leaf area density were identical in both cultivars during the ear initiation stage, because Milyang 23 had a slightly higher LAI than Asominori (Fig. 4), but after heading, Milyang 23 had a lower leaf area density. Milyang 23 showed higher value in relative light intensity (I/Io) in the canopy, resulting in a lower extinction coefficient (k) since the canopy of Milyang 23 consisted of erect leaves as compared to that of Asominori, and Milyang 23 had a higher angle of inclination with the upper leaves (Fig. 4, 5 and 6, Table 3). There was no significant difference in the photosynthetic rates (p₀) of the cultivars during the ear initiation stage.

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In a previous paper, we suggested that the sink capacity, defined as the spikelet weight with the exclusion of grain per unit leaf area at harvest, was too low to allow further increase in grain yield of rice varieties cultivated in the warmer part of Japan. In this paper, we compare the characteristics of grain production among old and new types of cultivars growing in the warmer part of Japan and improved japonica-indica hybrid cultivars such as Milyang 23 and Yoo Sin. Milyang 23 showed higher yields, higher total dry matter production and higher harvest index in plots with standard and heavy nitrogen application (Fig. 1). In all cultivars used in this experiment the sink capacity and leaf area increased following heavy nitrogen application (Fig. 2). It was remarkable that both Korean cultivars had a larger number of spikelet per unit leaf area (49, 000/m²) as compared with the Japanese cultivars (37, 000/m²) (Table 1). This difference was ascribed to variations in the number of spikelets per ear between Japanese and Korean cultivars. The Korean cultivars showed a lower increase in leaf area and a higher increase in sink capacity in relation to nitrogen absorption during the period from transplanting to heading (Fig. 3). The sink/source ratio, representing the ratio of sink capacity to leaf area at heading, was much higher in both Korean cultivars than in the Japanese cultivars (Table 2). Among the Japanese cultivars the old types had a higher ratio because they had larger ear than the new types of cultivars (Table 2). Therefore, it is considered that the Korean cultivars can produce ears with higher sink capacity without displaying excessive leaf growth. As a result, the harvest index remained high when total dry weight increased following heavy nitrogen application (Fig. 1). The Korean cultivars, with short culm and large ears, showed two interesting feature, as follows; compared with the Japanese cultivars their sink/source ratio was higher than that of old types although they had the short culm of the new types of cultivars. However, since the Korean cultivars have several disadvantages related to taste and tolerance of disease and cold, it will be necessary to develop new cultivars showing with the advantages of the Korean cultivars, while minimaizing their shortcomings.

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[in Japanese]

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It is important to analyze the plant growth not only from the responses of above ground organs of the plant to various spatial environmental conditions, but also from the processes of mineral uptake by roots at the same time. In the present paper, I discussed the relationships between the derivates which composed the root growth analysis and the growth functions by which the growth analysis was constituted. The cultivar of Oryza sativa L., Koshihikari, was used for the experimental material. As the treatments, five nutrient levels, NO₃-N : 5, 10, 25, 50 and 100 ppm, were employed in the experiments. Whole dry weight, top dry weight, root dry weight, plant height, leaf area, number of tillers, number of roots, maximum root length and α-naphtylamine oxidizing activity in the roots were measured. The values of URA (Unit root activity=Ra/Rw : Ra is α-NA oxidizing activity per plant per hour, Rw is root dry weight), RWR (Root weight ratio=Rw/Pw : Pw is plant dry weight), RAR (Root assimilation rate=1/Ra·dPw/dt), were calculated by the procedure proposed by KUJIRA and KANDA which was descrived in the previous paper. The positive correlations were observed between URA and LAR (Fig. 7), and between URA and RGR (Fig. 6). The RWRs indicated the positive correlations to the LARs in the 50 and 100 ppm-N nutrient levels, but this correlations, on the contrary, were negative in the 5, 10 and 25 ppm-N nutrient levels (Fig. 8). It was recognized that the derivatives composed the root growth analysis and the growth analysis were interdependent mutuality in substance.

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Rice seeds coated with calcium peroxide can emerge under anaerobic condition such as in the soil of submerged paddy field. The seedling elongates the coleoptile first and then develops a seminal root and foliage leaves. The same feature of elongation was observed with a hulled rice seedling that grew in the agar medium (Fig. 1). In this paper, we report the anatomy of vascular bundle network distributed in the various organs at the early stage of emergence when mesocotyl achieved to grow. 1. On the transection of mesocotyl, there are two central cylinders, distinguished to large and small ones, and the former is located at the central part and the latter with the scutellum is at the dorsal side. The small central cylinder is a collateral vascular bundle composed of protoxylem and protophloem. In the vascular system of large central cylinder, we observed that both the vessels of protoxylem and the sieve tubes of protophloem lost their cytoplasmic content and these cells changed to pipe-like structure, whereas the cells of metaxylem and metaphloem were not matured enough to lack their content (Fig. 2). The observation indicates that only active conductive tissue consists of protoxylem and protophloem. Protoxylem and protophloem failed to acquire a characteristic arrangement as collateral vascular bundle, and scattered randomly, and this fact has not been reported hitherto. 2. Therefore, we traced the orientation of the protoxylem and protophloem strands in the various organs, mainly mesocotyl (Figs. 5-16), and thus obtained a schematic figure of the whole structure of network as shown in Fig. 3. The protoxylems and protophloems of radial vascular bundle in the seminal root were gathered in a block at the node with their characteristic orientation. Just above the gathering point, protophloems were separated into two directions, one on the dorsal side and the other on the ventral side, while protoxylems remained unseparated. The protoxylems and protophloems were distributed independently in the large central cylinder of mesocotyl. At the coleoptile node, the protoxylems and protophloems ran separately in several directions and then formed collateral bundles which were not found in the lower part of large central cylinder. One of them ran in the reverse direction and then into the scutellum, while the others formed coleoptile and foliage leaf bundles. 3. From these observations, the authors conclude that the large central cylinder of mesocotyl is a transitional tissue system before the radial vascular bundle of seminal root shifts to the collateral vascular bundle of the stem and leaf. Thus, the mesocotyl is an organ that functions as hypocotyl of dicotyledon.

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In the previous reports^{4, 5, 7}), a difference between the leaf water potential (Ψ_l) measured by thermocouple psychrometer and the xylem water potential (Ψ_x) by pressure chamber was found in rice plants under intense transpiration, and it was considered that Ψ_l represented physiological leaf water status, but Ψ_x did not always represent it. The present study was conducted to investigate the interrelations of Ψ_l or Ψ_x among leaves on the different position of a stem and to discuss the changes in water status in rice plants under various environmental conditions. Ψ_l of leaves on the different position of a stem lowered equally under direct sunlight. Furthermore, there was no difference among their Ψ_l irrespective of water potential of soil and culture solution (Fig. 2, Table 1). After transfering the plants to the dark room from under direct sunlight, Ψ_l and leaf water content on an areal basis became higher in the dark room than those under direct sunlight. Moreover, Ψ_l in the dark room became higher than water potential of soil or culture solution when water potential of soil or culture solution was low (Fig. 1 and 2). In this case Ψ_l and leaf water content of upper leaves were higher than those of lower leaves (Fig. 2 and 3). From these results, we concluded that water was transported to leaves, especially upper leaves from soil or culture solution against the gradient of water potential. Ψ_x of leaves on the different position of a stem was not different both under direct sunlight and in the dark room, irrespective of water potential of soil and culture solution (Table 1 and 2). Ψ_x was always nearly equal to water potential of soil or culture solution in the dark room (Fig. 1, Table 2). Examining the relations between Ψ_l and Ψ_x in the same leaf of rice plants under dry soil, it was found that Ψ_l was higher than Ψ_x, i. e. water potential of mesophyll was higher than that of xylem in the dark room as well as under direct sunlight. The difference between Ψ_l and Ψ_x was larger in upper leaves (Fig. 2, Table 1 and 2). But Ψ_l became to be closed to Ψ_x gradually as time went by after transfering the plants to the dark room (Fig. 4). We examined the effects of treating roots and leaves with NaN₃ on Ψ_l and Ψ_x in rice plants under solution culture in the dark room. Ψ_l in plants with roots treated with NaN₃ was lower than that in control plants, but it was still higher than water potential of culture solution (Table 3). Ψ_l of leaves treated with NaN₃ was lower than that of control, and was not higher than water potential of culture solution (Table 4). We could not find any significant effects of treating roots or leaves with NaN₃ on Ψ_x (Table 3 and 4). From the results mentioned above, it is considered that water transport to leaves from soil or culture solution against the gradient of water potential depends on the physiological activity in leaves rather than in roots, and that water transport to mesophyll from xylem against the gradient of water potential depends on the activity of mesophyll in leaves. Thus it is clarified that physiological activity in leaves, especially mesophyll plays an important role in absorbing water into leaves against the gradient of water potential. Then it is assumed that the difference among Ψ_l in leaves on the different position of a stem may be brought about by water transport ability of mesophyll against the gradient of water potential. [the rest omitted]

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Developmental processes of the endosperm in two-rowed barley were investigated. Special attention was paid to the peripheral region of endosperm, because the reserve substances were taken into the endosperm through them. Noticeable modifications of cell shape in the endosperm parenchyma, aleurone and subaleurone were found, and they were discussed in relation to taking in or translocation pathway of the reserve substances as ripening advances. During 7th to 12th day after anthesis, especially in 11∼12 day, endosperm parenchyma cells locating at some distance to the periphery showed remarkably irregular modification (Fig. 3). This irregularity was backed to normal as the cells began to store starch grains. The period of modification is the same with the maximum period of the ratio of translocated dry matter to the kernel dry matter in weight (Fig. 1 C). The indented modification was more prominent in the periclinal cell wall than in the anticlinal one. So the area of periclinal boundary between cells increased by 2∼3 times. It seems to be right to consider that the modification has some adaptive function to the translocation from peripheral to inner portion of the endosperm. During 13th to 16th day, the indentation appeared in the cell walls of aleurone (Fig. 4). This period is the rapid increasing stage of reserve substances per day (Fig. 1 B), and nucellar epidermis was in the climax in development. The indentation of aleurone cells may be useful to help the effective acception of reserve substances from nucellar epidermis, then send to inner portion through it. During 17th to 29th day, especially in 17th to 22nd day, subaleurone cells changed their shape to floral-pattern mosaic (Figs. 5, 6 and 7). However they were restored to the normally round shape as they were filled with starch and protein grains (Figs. 8 and 9). This period is in accord with the maximum term of increase of reserve substances per day (Fig. 1 B). Nucellar epidermis already degenerated, and acception pathway of reserve substances had been limitted to the dorsal portion where the transfer cells come near completion of development at this time as reported in the previous paper. In the later stage of ripening, reserve substances accepted might be sent from dorsal portion to the flanks and ventral portion through the subaleurone cells where starch grains are not yet stored. It seems to be adequate to consider that modification of subaleurone cells is an adaptation to the translocation, because the increase of wall area of individual cell by the indentation ranged in 1.6 to 2.1 times, but it is especially high (2∼3 times) in the anticlinal cell walls.

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In this report, breaking resistance, structures and cell wall components of lower internodes were studied in rice plants, var. Koshihikari, grown in several different environments, which implied the effects of natural lodging, heavy manuring, shading or tiller cut as described in Table 1. In the experimental plots of the natural lodging, the heavy manuring and the shading, most of the plants lodged with the breaking of spindly grown lower internodes (Table 1). The plants in the lodging plots had longer culm or longer lower internodes, smaller breaking strength, less developed EF (epidermis-cortical fiber compound) and less quantity of dry weight, lignin and ash contents per unit length of lower internodes than the plants in the unlodging control plots (Tables 1-4, Figs. 1 and 2). The plants in the heavy manuring plot had thick lower internodes in diameter as the result of favourable growth untill the tillering stage, but their value of d²t, (diameter of of internode)² × (thickness of EF), was smaller than that in the control plot because of over-luxuriant growth in the time of internodal elongation and poor development of EF (Table 2). The lower internodes of the plants in the tiller cut plot, on the other hand, had sufficiently all the characteristics to increase the breaking resistance, namely, thick EF, thick cell wall, large diameter and large value of d²t, short length of epidermal cells and fundamental parenchyma cells, long fiber cells, and large amounts of dry matter, lignin and ash per unit length (Tables 1-4, Figs. 1 and 2). In order to develop the lower internodes with the structural characteristics indispensable to powerfull breaking resistance as shown in the plants of the tiller cut plot, it is necessary to realize the following items, (1) inhibiting the lower internodes from spindly growing by full exposure to sunlight, (2) increasing the photosynthetic ability of each tiller, and (3) increasing the amount of dry matter per unit length of lower internodes.

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[in Japanese]

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The type of cracking of seedcoat and the percentage of seeds having cracked seedcoats were investigated on the seeds of 104 cultivars of soybean which were collected from 34 prefectures all over Japan, and also on the seeds of 53 cultivars which were grown in our experimental farm, in order to clarify the actual condition of cracking of seedcoat in soybeans. 1. The type of cracking of seedcoat was classified into three types, i.e. spot type, line type and irregular type (Fig. 1). Fifty three cultivars out of 104 cultivars used in this investigation were spot type, 27 cultivars were irregular type, and only 18 cultivars were line type (Table 1). 2. A marked difference was found among cultivars in the percentage of seeds having cracked seedcoat, and the mean value of the percentage in 104 cultivars was 25.0±24.8 per cent, which ranges from 0 per cent at the minimum to 100 per cent at the maximum (Fig. 3). The cultivars which has no cracked seedcoat were only six, three in Hokkaido and each one in Iwate, Niigata and Nagasaki prefectures, respectively. The cultivars which has below 10 per cent of seeds having cracked seedcoats were 38, and the cultivars which has above 50 per cent of seeds having cracked seedcoats were 15 out of 104 cultivars. 3. Regional difference was also found in the percentage of seeds having cracked seedcoats. It was the lowest in the seeds harvested in Hokkaido with 3.7 per cent, and was lower in the seeds harvested in Kanto-Tosan and Kyushu with 14.6 per cent and 19.2 per cent, respectively. On the other hand, it was the highest in the seeds harvested in Chugoku with 43.4 per cent and was higher in Tokai, Hokuriku and Shikoku with 41.6 per cent, 35.4 per cent and 33.3 per cent, respectively (Table 1). 4. In the same cultivars, the percentage of seeds having cracked seedcoats also differed in the regions where the seeds were harvested (Table 2). 5. In the seeds of cultivars harvested in the experimental farm at Kakamigahara, it was found that the percentage of seeds having cracked seedcoats increased in the seeds of cultivars collected from the regions showing lower percentage of seeds having cracked seedcoats, and the percentage of seeds having cracked seedcoats and the weight of 100 seeds decreased in the seeds of cultivars collected from the regions showing higher percentage of seeds having cracked seedcoats (Table 3). 6. No correlation was fonud between the percentage of seeds having cracked seedcoats and the percentage of seed germination, and the weight of 100 seeds. But negative correlation was found between the percentage of seeds having cracked seedcoats and the thickness of seedcoats, and the percentage of seedcoats (Table 4 and Fig. 4).

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The productive structure and the light distribution characteristics at early ripening stage in mixed-sowing community of rice were examined at two fertilizer levels on well drained paddy field. And the relationships between their results and lodging resistance, or and matter production were discussed. Two cultivars 'Koshihikari', tall and lodging-susceptible, and 'Kanto No. 100', short-statured and lodging-resistant, were used. Both of them are of the same maturity. Koshihikari and Kanto No. 100 were sowed alternately to two rows and two rows, or one and one, respectively. 1. The effects to mixed sowing on productive structure under one row alternate mixture were more remarkable than those under two rows alternate mixture. The fresh weight of assimilatory and nonassimilatory organ increased by mixtures in the upper layer of structure in Koshihikari and decreased in the middle-low layer in Kanto No. 100. Consequently more increase of the rate of upper layer weight was recognized in the mixed stands involved two varieties, compared with the mean value of the pure stands of the two cultivars. 2. The light receiving structure of Koshihikari obviouly was made better on all layers in mixtures and that of Kanto No. 100 was made worse except on lower layer. However, the light receiving structure of mixed stands involved two varieties was clearly better than that of pure stands of Koshihikari, but not beyond Kanto No. 100, and it was superior to the mean structure of the pure stands of the two cultivars. These suggest that 'the active effect of cooperation' was appeared in the light receiving structure. Those results were confirmed by usual comparison methods of the productive structures and the extinction coefficient K. Furthermore, the vertical light receiving distribution was able to be compared relatively and quantitatively to some degree by using light receiving index (relative illuminance ×leaf area index of each stratum) proposed in this report. 3. It was considered that the intensification in lodging resistance (such as the increase of the breaking strength) of Koshihikari by mixed sowing was closely related to the improvement of the light receiving structure at the early ripening stage through the maintenance of activities in the leaves and leaf sheathes occurring at the lower nodes. 4. The crop growth rate (CGR) and the net assimilation rate (NAR) during ten days after the investigation of the production structure were correspondent with the quality of the light receiving structure. The CGR and the NAR of Koshihikari increased in mixtures and those of Kanto No. 100 decreased, however, those of mixed stands involved two varieties were larger than the mean value of the pure stands of the two cultivars. In those growth parameters the active effects of cooperation were also recognized. 5. The artificial condition of no lodging was set up through stretching a net. In the top dry weight the active effects of cooperation were recognized correspondingly with those in the light receiving structure, but those effects were not recognized in the yield. Therefore, it seemed to be difficult to gain the active effects of cooperation for the yield by mixed sowing without the secondary effects such as the prevention of lodging that the improvement of the light receiving structure accompany.

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The relationship between hill size (number of seedling stems per hill) at transplanting and yield of the long stems was studied with two mat rush cultivars, i.e. Asanagi (tiller type) and Shimomasuda-zairai (elongation type). Two plots, i.e. a large hill size plot and a small hill size plot, were arranged for each cultivar. The large hill and the small hill consisted of 10 stems-10 buds and 3 stems-3 buds, respectively. The process of tillering, stem elongation and dry matter production were analysed. The results are summarized as follows : 1. In both cultivars, number of stems per hill, dry weight per hill and stem surface area index (SAI) in the large hill size plot gradually increased from the early stage of the growing season to the harvest time. However, in the small hill size plot, these growth parameters began to increase about one month later than the large hill size plot, and markedly increased from the middle of April to the middle of June, then reached a maximum about 20 days before the harvest time. 2. In Asanagi, net assimilation rate (NAR) in the large hill size plot gradually decreased from the beginning of March to the harvest time, while NAR in the small hill size plot began to increase rapidly in the beginning of March, then reached the higher level than that of the large hill size plot, but decreased faster than in the large hill size plot, and consequently NAR in this plot was lower than that of the large hill size plot after the beginning of July. Crop growth rate (CGR) in the small hill size plot was lower than that of the large hill size plot before the beginning of May and after the beginning of July. The differences in the changes of these parameters between the large and the small hill size plot were almost similar in both cultivars. 3. Tillering behavior of both plots in Asanagi was similar. However, in Shimomasuda-zairai, tillering behavior was qualitatively different, because the 3rd nodal tillering as compared with the 2nd nodal tillering was weaker in the small hill size plos than in the large hill size plot. 4. The long stems of the small hill size plot mainly consisted of the tillers having 1 or 2 lower order positions and being shorter than those of the large hill size plot. The long stem yield of the small hill size plot was 28 percent lower than that of the large hill size plot. 5. In Asanagi, the tillers on the same order position elongated in the similar behavior, and the tillers on the 12th to the 17th position in the main tillering group had the characteristic to elongate faster and to become the longer stems. The elongation rate and the length of the tillers emerged after the latter part of May were closely related to the level of CGR after the end of June. 6. These results would show the reasons why much attention has to be paid to the degree of growth at the tillering stage of the long stems in the cultivation of mat rush.

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[in Japanese]

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