By means of the "leaf-cutting" method and under different light conditions, the relationship between the growth of crown roots and their branching habit was investigated in rice plants. Under shaded condition, as compared with the control, both diameter and growth rate of crown roots decreased remarkably, while the decreasing rate per day of their diameter remained almost constant. Irrespective of the differences in light conditions, a close correlation was found between the branching habit and the growth characteristics of crown roots. Namely, the density of laterals was higher on the crown roots, in which the diameter as well as growth rate decreased more rapidly, as exemplified in crown roots grown under shaded condition. In such crown roots, however, the total number of laterals formed within a definite time interval tended to be less, due mainly to the limited growth rate of the crown roots.

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The varietal differences and the interrelationships in transition of the characters related to lodging resistance after the heading were examined in direct sowing on well-drained paddy field. Four varieties differing in lodging resistance (i.e. Koshihikari, Yamakogane, No^^-rin 25 and Kanto^^- 90) were grown at two seeding densities. On the other hand, the effects of nitrogen top-dressing at full heading stage on lodging resistance were examined. 1. The decrease of lodging resistance after heading could bc attributed to the decrease in breaking strength and to the raise of the centroid height of the culm. 2. The decrease in the breaking strength after the heading had closer relationship to the decrease in the strength of leaf sheath than that of culm. 3. In the short-culmed variety, the contribution rate of leaf sheath to the breaking strength amounted to about 50% and this value maintained during about 30 days after the heading. However, in the long-culmed variety, thc rate was in the range of 30% to 40% and in lodging susceptible variety 'Koshihikari', the rate decreased rapidly after the heading. 4. The relative amount of starch in the breaking internode (the lowest internode over 6 cm long) decreased rapidly after the heading in thc lodging susceptible variety. Positive correlation coefficient was found between the amount of starch in the culm and the number of living leaf sheath wrapping the internode. 5. After heading, the number of living leaf and leaf sheath in the long-culmed variety were much the same to those in the short-culmed variety. However, the breaking internode of the long-culmed variety was one internode lower than that of the short-culmed variety, therefore, both the contribution rate of leaf sheath to the breaking strength and the starch amount of the culm in the long-culmed variety were less than those in the short-culmed variety. 6. By the top-dressing of nitrogen at full heading stage, the leaves and leaf sheathes of the lower internode were made alive longer. Consequently, it is considered that this treatment showed positive effect to lodging resistance through thc maintenance of breaking strength.

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[in Japanese]

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[in Japanese]

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In the extremely cool summer in 1980 (Fig. 1), rice plants grown in Touhoku District (the north-eastern parts of Honshu) suffered from the severe sterility due to the cool temperature at the booting and/or flowering time. The distribution pattern of coolness in Touhoku District at the extremely cool summer was estimated by the degree days of coolness, Σ(20-T), for five days from July 15 to 19, 1980, on which the high atmospheric pressure at 0khotsk Sea influenced (Fig. 2). Spikelets sterilities were recorded on some rice cultivars at 22 agricultural experiment stations located in main rice planting areas in Touhoku District. Daily changes of sterility were classified into five types (Fig. 3). Touhoku District was geographically divided into five areas according to the relative grades of danger caused by sterility type of cool injury of rice plants, which were estimated firstly from the types of the daily change of spikelets. sterility, and secondly from the degree days of coolness, altitude and topographical characteristics (Fig. 4). The relative grades of danger caused by sterility type of cool injury should be utilized for selecting the rice cultivars with the appropriate degree of resistance to cool-weather, though the relative grades of danger caused by delayed growth type of cool injury has been utilized for establishing the standard cultivation method and for choicing the rice cultivars with adapted maturity.

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[in Japanese]

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[in Japanese]

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The differences of productivity among the three crops were analyzed in terms of radiation absorption and its efficiency for dry matter accumulation, using the data obtained in the dry matter production-population density experiments reported previously^{12, 13, 14)}. In this experiment, photosynthetically-active radiation (PAR) intercepted by plant canopy (ΔPAR) during the experimental period (t₂-t₁) was calculated as ΔPAR=Σ^^(<SUB)2>__(i=t<SUB)1>0.444·S_i(1-exp^Ks.LAIi) where 0.444 is the proportion of full spectrum radiation in the range 400 to 700 nm; S_i is daily solar radiation; Ks is light-interception coefficient; LAI_i is daily value of leaf area index calculated assuming that LAI increased exponentially from t₁ to t₂. Light-interception coefficient was given by I/I₀=exp^-Ks.LAI where I₀ and I are the light intensities at the top and bottom of canopy, respectively, and the Ks value of each variety was estimated from the data measured three times for five population densities during the middle period of the growing season. The efficiency of dry matter accumulation per unit PAR intercepted (E_PAR, dry weight mg/kcal) during the experimental and/or full growing period was defined as E_PAR=ΔW/ΔPAR where ΔW is dry matter production and ΔPAR is the amount of PAR intercepted. E_PAR also could be described as E_PAR=NAR/(ΔPAR/(LAI)^^^-·Δt) [(LAI)^^^-=LAI₂-LAI₁/ln (LAI₂/LAI₁)] where NAR is net assimilation rate; LAI is mean leaf area index; Δt is number of days between t₁ and t₂; LAI₁ and LAI₂ are leaf area indices at times t₁ and t₂, respectively. The main results obtained are summarized as follows: 1. The maximum dry matter production for azuki bean and kidney bean was about 50-60%, on average, of that for soybean (Table 1). The maximum values for CGR, LAI and E_PAR during growing season were higher in soybean (Table 2), indicating highly positive correlations with the maximum dry matter production (r≥0.898**). 2. When plotted disregarding crops, varieties and densities, dry matter production hag significantly positive correlations with ΔPAR and E_PAR, while it was related positively only with LAD, and negatively with NAR. The regression of dry matter production on ΔPAR differed between two groups, one group's values of E_PAR were lower and the other higher than about 9 mg/kcal (Fig. 1). In addition, a simple correlation coefficient between ΔPAR and E_PAR was not significant, but a partial correlation between them was highly negative (Table 3). 3. The differences in total and pod+seed dry weight produced during grain filling period were in the same order as that exhibited in thc maximum dry matter production (Table 4). During grain filling both total and pod+seed dry matter production increased curvilinearly with increase of ΔPAR, but linearly with E_PAR. Takarashozu differed from this relation because it did not reach the LAI value required for 95% light interception except under the highest density (Fig. 2). 4. The very close regressions of CGR on E_PAR were found among the stages with different mean solar radiation, disregarding crops, varieties and densities, for which LAIs are more than the value required for 90% light interception (Fig. 3 and Table 6). A close correlation was also found between CGRmax. calculated by WASTON's method and E_PAR (density mean) (Fig. 5). 5. [the rest omitted]

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The changes of the diameter of the primary roots along their axes were investigated in corn plants in relation to the diameter and the density of lateral roots. The primary roots of the basal "shoot units", are formed earlier and those of the upper "shoot units" are formed successively later in the growth of the plant. In the basal "shoot units", the primary root diameter was relatively small and was almost uniform in any region of the axes. Whereas in the upper "shoot units", it was very large in the proximal regions, decreasing remarkably toward the root tips to the similar diameter as the basal "shoot units". Along with these changes in the diameter of the primary roots the average diameter of laterals formed on the primary roots also changed. That is, in the basal "shoot units", the average lateral root diameter was small and was almost uniform along the primary axes. However, in the upper "shoot units", it was large in the proximal regions of primary roots and decreased remarkably toward the root tips. The density of laterals was higher on the primary roots of the upper than on the basal "shoot units". Along a primary root axis toward the tip, it increased remarkably near the basal part and further was alomst uniform. Consequently, it was shown that the corn root system is composed of various kinds of primary roots, and the formation of the laterals is closely correlated with the diameter of the primary roots on which they are formed.

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Two observations were made. Firstly, growth and fine structures of cotyledons of ripening soybean seeds under high and normal temperatures were compared under light microscopy and electron microscopy. Secondly, changes of fine structure of cotyledons during germination, emergence and yellowing were observed. Soybean used is cv. Miyagishirome. The mean day/night temperatures were 35°/30°C (high temperature) and 24°/19°C (normal temperature). The results obtained are summarized as follows: 1. The seed maturity at 24°/19°C was about three weeks faster and 100-seed weight was greater than those at 35°/30°C. The number of seeds ripened per plant was almost the same between the two on account of very high sterility at 35°/30°C, although the number of pods per plant was greater at 35°/30°C (Tables 1 and 2). 2. The number of cell layers in both lengh and width directions of cotyledon was greater at 24°/19°C than at 35°/30°C, but that in thickness in opposite. The mean cell length of matured cotyledon was greater at 24°/19°C than at 35°/30°C, but the mean diameter was smaller at 24°/19°C (Tables 4 and 5). 3. Carbohydrate concentration (sugar+starch) was higher at 24°/19°C than at 35°/30°C, but protein concentration in opposite (Table 3). 4. The number of starch granules was most abundant in late ripening periods (Sep. 27 at 24°/19°C and Oct. 16 at 35°/30°C. At maturity they were almost disappeared from all parts at 35°/30°C and from abaxial parts at 24°/19°C. A few thylakoids appeared among starch grains during ripening period. Protein body was small at early ripening period, then became amoeba like at middle and late ripening periods, and grew up to bigger, round bodies at maturity. Mary endoplasmic reticulums were observed in adaxial parts of the cotyledon at middle and late ripening periods. Lipid spherical bodies were packed reticulately among the protein bodies just before maturity (Figs. 1-32). 5. The partitioned protein granules appeared in parenchyma cells of the cotyledon germinated but remained in the soil, and lipid bodies were almost disappeared at this time. In completely emerged yet folded cotyledon, thylakoid formation and starch deposition preceeded at abaxial part, but after unfolding they became more prominent at adaxial part, suggesting a light reception be concerned (Figs. 33-35). When cotyledon turned yellow, thylakoids were separated to form numerous vesicles (Fig. 36). These procedures seemed to proceed faster in abaxial parts.

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Previously, silica and potassium were shown to accumulated in the hulls of fertile grains than those of sterile ones. Based on these findings, effects of supplying of silica and potassium during reproductive growth stage on the form and function of hulls were further studied. And the effects of top dressing of new fertilizer "potassium silica" were also investigated. 1. Silica. (a) No significant difference in the number of spikelets on the primary branches of panicle was detected between no-supplying and supplying plot, whereas the number of spikelets on the secondary branches was increased by the supplying of silica. (b) Ripening percentage and weight of 1000 kernels increased significantly by supplying of silica. This might be due to the increase in the size of hulls and the decrease in the occurrence of malformed grains. (c) The silica content in hulls increased greatly by the supplying of silica. 2. Potassium. Supplying of potassium during reproductive growth stage gave mostly the same effect as those of silica, however the difference in potassium content was very small between no-supplying and supplying plot. 3. New fertilizer "potassium silica" The top dressing of potassium silica, a new fertilizer, at initial stage of spikelets differentiation enhanced the ripening percentages and weight of 1000 kernels due to the decrease in the occurrence of malformed grains. As shown above, silica and potassium affect the form and function of hulls and were very useful and important to increase ripening.

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Starch accumulation and lignin formation with relation to several enzyme activities n hulls were studied with fertile and sterile grains during ripening. 1. Starch accumulation could not be observed in the hulls of sterile grains during ripening. However, in the hulls of fertile grains, that was observed at early and middle stage of ripening, although it disappeared thereafter. 2. Lignin formation could not be almost observed in the hulls of sterile grains during ripening, whereas it proceeded in the hulls of fertile grains with ripening. 3. In the hulls of fertile grains, the activity of amylase was lower and that of phospholylase was higher than in those of sterile grains during ripening period.4. Peroxydase activity was much higher in the hulls of fertile than in those of sterile grains. From these results, hulls might play several roles not only as a pool of mineral elements and carbohydrates as shown previously but also as the protector of kernels. The physical strength or hulls may increase through several biochemical progress which triggered by the fertilization as shown in this report.

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In this paper, we report an observation with light and electron microscope on the process of the secondary wall thickening and lignin accumulation in the cells of the 4th internode from the top of rice culm, var. Koshihikari. Materials for ultra thin sections were fixed in 2-4% glutaraldehyde, postfixed with 1-2% osmium tetroxide, and embedded in Spurr's resin. Meshes were stained with uranium and lead. For histochemical detections of lignin, free hand sections, 60-80 μm in thickness, were treated with Maule's reagents (M-reaction) and phloroglucinol-HCl (P-reaction). The secondary wall of the cortical fibers makes a start of thickening just after the cell has completed its elongation. It usually consists of three layers; S₁, S₂ and S₃. In crease in secondary wall thickness is associated with increase in number of Golgi apparatus, Golgi vesicles, exocytosis and invagination. The ribosomes are often present as polysomes on the rough endoplasmic reticulum, some of which connect with the plasmalemma (Figs. 1-4). The fiber cells have smaller diameter and thicker walls in the outer rows near the epidermis than those in the inner rows which sometimes lack S₃ layer. The secondary walls of the tips of fiber cells thicken more slowly and are thinner than those of the central part (Fig. 5). The epidermal long cells have a large number of small papillae, and a number of large ones on both sides of the short cells, but a fewer papillae on the small vascular bundle (Fig. 6). The aspects of cell organelles at their wall thickening stage are similar to those in the cortical fibers (Figs. 8-10). At this stage, silica deposition cetripetally progresses from the inside of cuticular layer in all the outer walls of the long cells, especially in those of the silica cells (Figs. 9-12). As for the parenchyma cells, a large vacuole is formed from an early stage of cell development, and conspicuous invaginations are often seen accompanying with ribosomes (Fig. 13). No lignin is detected in elongating cell walls except those of the protoxylem vesseles. On and after beginning of the secondary wall thickening, M-reaction begins by appearing (Fig. 14A). On and after beginning of the S₂ layer thickening, P-reaction follows up the traces of M-reaction. M-reaction decreases in the part where P-reaction is positive (Fig. 14B). In the 4th mature internode, P-reaction is generally intensive in thc epidermis, cortical fibers and small vascular bundle. M-reaction is thc most intensive in the large vascular bundle sheath (Fig. 14C). In a fiber cell, P-reaction is the most intensive in the middle lamella-primary wall complex and decreases centripetally. On the contrary, M-reaction is intensive on the faint parts of P-reaction, but both reactions are not obvious in the parenchyma. In briefly saying, P- and M-reactions relate complementally each other. The secondary wall thickening and the lignin accumulation in the 4th internode of the cultivar terminate about 5 days after heading and entirely complete after next 10 days.

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The external breaking forms of elongated internodes in rice culms were observed, and were classified into three patterns basically, namely, the broken type (Fig. 1), the split type (Fig. 2) and the separated type (Fig. 3). The broken type was the most frequent in the lower internodes both in the breaking test by hands and in the lodged culms by natural force like as wind and rain (Table 1). Histological observations on the breaking parts by free hand sections indicate that the breakings seem to begin from the epidermis and cortical fibers and extend to parenchyma. In fold parts of the broken type failure, the cortical fiber cells are bent remarkably and divided longitudinally in each other, but are not cut off transversely (Figs. 4-7). In split parts of the broken and the split type failure, most of the epidermal and cortical fiber cells are divided in middle lamella. The parenchymatous cells in breaking parts are broken irregularly (Figs. 8-10). A dynamic consideration is attempted to clarify the mechanism which causes the three patterns of the breaking forms in the lower internodes. In a bent internode, bending stress and shearing stress seem to cause as illustrated in Figs. 11 and 12. Therefore, the compressive stress acting on the concave and the tensile stress acting on the convex seem to cause the failure of the broken type and the separated type, respectively. The shearing stress, on the other hand, acting on the transverse plane seem to cause the failure of the split type (Figs. 11 and 12).

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