During callus induction, auxin uptake and metabolism in rice seeds were investigated with ¹⁴C-carboxyl-labelled 2, 4-D and IAA. The uptake and metabolism in rice callus were compared with tobacco and barnyardgrass callus cultures. Radioactivity of 2, 4-D absorbed in the callus cultures and rice seeds was high in the 80% ethanol fraction and low in the residual fraction but scarce in the gas phase, expected to contain CO₂ owing to the decarboxylation. Two kinds of 2, 4-D metabolites were present in the 80% ethanol fraction extracted from rice seedlings, rice callus and barnyardgrass callus. Inhibitory activities of them were lower than that of 2, 4-D in the growth test with rice seedlings. It seems that they are different from 2, 4-D-aspartic acid on the base of Rf value of chromatogram. From the quantitative research on 2, 4-D and 2, 4-D metabolites, it was shown that the tissues inducing callus contained higher level of 2, 4-D than those which had not induced callus. The barnyardgrass, which had required high concentrations of 2, 4-D for callus induction, contained high level of 2, 4-D metabolites but low level of 2, 4-D, when compared with rice callus. Therefore, it is assumcd that 2, 4-D level plays an important role in callus induction on the tissues. In ricc callus, most of IAA was converted to IAA-aspartic acid or degraded into CO₂. Requirement of high concentration of IAA in rice callus for callus induction and subculture seems to be caused by faster degradation and inactivation of IAA than those of 2, 4-D. It is probable that 2, 4-D directly acts to the callus induction but not via IAA production by 2, 4-D, because the level of IAA, which would be required for callus induction, was not found in the 2, 4-D treated rice tissues. And also, selectivity of 2, 4-D as a herbicide is dis-cussed here in the relation to 2, 4-D metabolism in plants.

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Using several rice varieties of rice ecotypes, Aman, Aus, Bulu and Tjereh, including Japonica varieties, it was attempted to clarify the relationships between the leaf area growth, light-saturated photosynthetic rate and soluble protein level, and furthermore to investigate the assimilation of ¹⁵N-labelled ammonium nitrogen into the protein fractions in the leaf blades: The results obtained are as follows: 1. In the eleven rice varieties, it was found that there was negative association betwecn single leaf area and light-saturated photosynthetic rate per unit leaf area. 2. The contents of soluble protein per unit leaf area in the leaf blades of the varieties which developed smaller single leaf area were much higher than those of the varieties which developed larger single leaf area. Accordingly, there existed strong negative association between single leaf area and soluble protein content in the leaf blades. This, in turn, appeared to being about the negative correlation between single leaf area and photosynthetic rate as described above. 3. The assimilation of ¹⁵N-labelled ammonium nitrogen was studied in the five rice varieties which were contrastive in the leaf area growth. As a result, it was concluded that fraction-1 protein among soluble proteins was accumulated greatly in the leaf blades of the varieties which developed smaller single leaf area as compared with those of the varieties which did larger single leaf area, because protein synthesis predo-minated over protein degradation in the upper leaf blades and protein degradation was suppressed greatly in the lower leaf blades.

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The purpose of this investigation is to clear the effect of farmyard manure (FYM) on the nitrogen uptake, the nitrogen fixing capacity and the seed yield of nodulating soybean. In order to estimate the amount of fixed nitrogen, nodulating and non-nodulating isogenic lines were grown at same condition in 1/5000 are Wagner pot containing 3 kg of mineral soil with some levels of FYM or urea. The results obtained were as follows. 1. It was observed at the flowering stage of growth that the inhibitory effect of FYM on the nodule formation was clearly weaker than that of urea, and the number of nodules, the fresh weight of nodules and the amount of fixed nitrogen per plant were the largest at the application of lower level of FYM (80g fresh weight per pot). The nitrogen fixing capacity per unit fresh weight of nodules at flowering stage also increased with the level of FYM, although the higher levels of FYM (200, 400 and 1200g per pot) were unfavorable for the nodule formation. 2. Such an inhibitory effect of FYM on the nodule formation gradually diminished with aging. It was also observed at the harvesting time that the application of FYM in the ranges of 80g to 400g per pot led to the increase in seed yields accompanied with the larger amount of fixed nitrogen and the higher ratio of secd nitrogen to total nitrogen uptake, without diminishing the ratio of fixed nitrogen to total nitrogen in plant. 3. It was therefore presumed from this experiment that the application of FlM resulted in the increase of seed yields through thc improvement of symbiotic nitrogen fixation rather than the supplemental supply of available nitrogen released from FYM.

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Investigations have been carried out to determine the effect of variety, field, and milling on the protein, crude fat (ether extract), combined fat (fat by acid-hydrolysis after ether extraction), total fat (crude fat and combined fat), ash, phosphorus, potassium, and magnesium content of lowland non-glutinous rice grain of 3 varieties cultivated at 9 experimental fields in Miyagi Prefecture. The average of variation value by milling, i.e. (milled rice/brown rice) × 100, on 3 varieties each is as follows: crude fat content: about 35%, total fat, ash, phosphorus, potassium, and magnesium contents: about 50%, and protein and combined fat con-tents : about 90%. As to the relation between brown rice and milled rice, positive correlations were observed in the protein content of 3 varieties each and the whole of 3 varieties, the ash content of one variety and the phosphorus and magnesium contents of 2 varieties each and the whole of 3 varieties. The variety had a significant effect upon the protein, crude fat, total fat, ash, and potassium contents of brown rice and upon the protein, crude fat, combined fat, total fat, and phosphorus contents of milled rice. On the other hand, the field had a significant effect upon the protein, crude fat, total fat, phosphorus, and magnesium contents of brown ricc and upon the protein, phosphorus, potassium, and magnesiumcontents of milled rice.

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Occurence of varietal differenccs in the protein content ot. brown rice were investigated with reference to some agronomic traits. The results obtained are as follows; 1. At the heading stage, LAI was smaller in earlier heading varieties than in later ones, but there was no difference in the numlber of spikelets per m² according to varieties' maturity. Accordingly the leaf area per spikelet was smaller in earlier heading varieties. So dry matter production per spikelet was less in these varieties. On account of this, ripening percentage became lower and the weight of kernel bccame lighter in earlier heading varieties. 2. On the other hand, at the heading stage, the nitrogen content of the plant body was higher in earlier heading varieties, but there was no difference in the nitrogenquantity of the plant body per spikelet according to the varieties' maturity. And the degression of nitrogen content of leaf blade during ripening period was greater in earlier heading varieties. 3. From these results, nitrogen accumulated in kernel relativey more than starch in these varieties, so that protein content became higher in these varieties. 4. Protein content increased by shading treatment during ripening period and the degree of increasing was higher in earlier heading varieties.

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The present studies were conducted to clarify the varietal differences of the radicle emergence under low temperature condition (15°C). The author used 46 new and old varieties which have been bred in Hokkaido and posses different degrees of germinability at low temperature. There were no seeds in which the radicle emergence of seminal roots preceded germination. The days from germination to the radicle emergence varied 2-4 days among all varieties and about 90% of the seeds commenced the radicle emergence at 6-8 days after germination. The plotted curves of the radicle emergence which began at 6-9 days and ended 12-14 days from seeding, closely resemble the plotted sigmoid curves in the germination at 15°C, although the initiation was delayed by 2-4days. Both the rooting coefficients and the number of days from germination to the radicle emergence indicated significant differences among varieties and the correlation coef ficients between both characters was highly significant showing r=-0.387. In contrast with this, a non-significant relation was recognized between the germination coeffients and the number of days from germination to the radicle emergence (r=-0.039). A partial correlation between the above characters was calculated by excluding thc effect of the germination coefficients and a highly significant value at a 0.1% level (r'=-0.919) was seen. It is assumed that the germination at low temperature are not always accompanied by the initiation of radicle emergence of seminal root which is controlled in such a way as to occur after the germination. Therefore it is possible that both characters are governed by different factors to some extent. Since a highly significant correlation existed between the germination and rooting coefficients (r=0.924), it seems to be of considerable importance that the varietal improvement promoting the germinability at low temperature may be effective for the selection of the high rooting ability which may lead to the breeding of a variety suitable for direct sowing floodcd paddy field in the cooler region.

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This investigation was conducted to make clear the physiological properties of dormant Bupleurum falcatum seeds in respiration, physiological changes of seeds during after-ripening period and after low temperature treatment. The results obtained are as follows; 1. Difference of respiratory quality was studied between undeveloped dormant seeds and five months old nondormant seeds to tests by checking the effect of an un-coupler (2, 4-dinitrophenol) in oxidative phosphorylation scheme. It was clarified that there was no relation between the high oxygen absorption of the dormant seed and energy production. This fact suggested that the high oxygen absorption by dormant seed was not related with respiration. 2. Changes of the RNA content and amylase activity were continuously measured for six months during the storage period. The both values were gradually increased.The highest values were observed at the fifth month. Therefore, the endosperm of Bupleurum falcatum seeds might be physiologically immature at the time shedding, and it might be gradually matured as the after-ripening is progressed during the storage period. 3. Low temperature treatment was applied to find the effect on RNA content and amylase activity. It was observed that after low temperature treatment, the seeds showed no changes as for RNA content but showed higher amylase activity.

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[in Japanese]

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[in Japanese]

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Developmental and anatomical features of soybean leaves grown under different photoperiod and temperature were compared in consideration for their relations to growth parameters. 1. Leaf number increased with increase of temperature and daylength. The leaflet size of the 5th leaf was greater under long day than under short day, and greatest at 25°C or 30°C day temperature. Thus, relative growth rate of leaf area per plant increased with increase of temperature and under long day condition. The thicknesses of leaf blade, mesophyll and pallisade layer, and specific leaf weight increased with decrease of temperature, whereas leaf area ratio decreased with decrease of temperature. 2. The volume of each pallisade cell increased while air-space percentage decreased with decrease of temperature. Pallisade tissue consisted of two layers of cells, being about twice as thick as spongy tissue and this situation was little affected by the treat-ments. 3. The mean area of epidermal cell was greatest at the intermediate temperatures, becoming smaller as temperature increased or decreased. It was greater under long day than under short day. Stomatal density was high at abaxial surfacc and low at adaxial surface, and the density of the latter increased with increase of temperature although that of the former changed a little. The mean length of guard cell parallelled the mean epidermal cell size. The total guard cell length of both leaf surfaces per unit leaf area increased with increase of temperature. 4. TAC concentration, TAC content per unit leaf area increased with decrease of temperature, and were greater under long day. Crude protein concentration, on the contrary, decreased with decrease of temperature and was smaller under long day, although its content increased with decrease of temperature and was greater under short day. 5. The diameter of petiole was greater under long day and greatest at 30/25°C. The number of large and intermediate vascular bundles of petiole changed little by the treatment, but that of small bundles increased with increase of temperature. The petiole diameter and mean area of large vascular bundles were intimately related to leaf area. 6. The starch deposit in the chloroplasts increased with decrease of temperature, especially abundant in the spongy tissue. Under low temperatures, large peculiar compound starch grains were stored in the parenchymatous cells of petiole and stem. 7. Anatomical features affected by temperature and photoperiod did not show significant correlations to NAR, although SLW, leaf thickness, nitrogen content and Sol-N/Total-N ratio had negative correlations with NAR. 8. SLW had positive correlations with both leaf thickness and TAC concentration, a negative correlation with air-space percentage. 9. The growth parameters such as RGR, RLGR, LAR and NAR were all positively correlated with the mean ambient diurnal temperatures, and the correlation coefficients were higher for RGR, RLGR and lower for NAR.

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Grain growth, translocation of assimilates to the ear and photosynthesis are important processes to contribute to the formation of grain during the period of grain-filling in cereal crops. The objective of this investigation was to identify, for rice, which of these three proecesses is most affected by the water stress developed in grain-filling Perlod. We grew rice plants (Oryza Sativa, L. cv. Nipponbare) singly in 4 litter pots under outdoor conditions. The pots were kept flooded untill 15 days after anthesis. Then we transferred plants in a vinyl-covered house and stopped watering half the plants (deslccated). The rest of the plants were kept watered (control). Just before treatment, plants had their tillers removed to have four culms of approximately the same age. Plant water status was determined in terms of relative water content (RWC), being supplemented by measurements of the stomatal aperture and the transpiration rate. Plants were harvested before and after treatment, and dry weight was determined for unhuIled rices, rachis, top internode, lower internodes, leaf blades, leaf sheaths, crowns and roots. Progressive decline in RWC was more evident in plants subjected to soil desiccation. The change in stomatal aperture and transpiration rate with time also indicate that more severe stress developed in desiccated plants. But, there was little difference in dry weight increase in unhulled rice over 10 day period between control and desiccated plants, though the increase of total dry matter was reduced significantly in desiccated plants. This was accompanied by the greater decrease in dry weight of non-grain parts in desiccated plants. We therefore conclude that the water stress during the rapid growth of grain has little effect on grain growth as well as translocation in rice, while it reduces the rate of dry matter production considerably.

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The object of this study is to investigate the differences in dry matter production, plant type and productivity in soybean (Glvcine max Merr.), azuki bean (Vigna angularis) and kidney bean (Phaseolus vulgaris L.). For the first trial of this study, dry matter accumulation patterns of three crops including twelve varieties were compared under the low population density (60cm × 45cm, singling). The results obtained were summarized as follows: 1. Varietal differences in dry weight of vegetative portion were cleared up after about the initiation of flowering in each crop. Indeterminate types of soybean and kidney bean, and late varieties of azuki bean produced more vegetative matter than determinate and early ones. 2. The distribution ratio of dry matter to leaves was the highest in the early growth stage and gradually declined with time in all varieties. However, some of them were found to show a peak at the initiaI branch-elongation stage just before the flowering. 3. The distribution of dry matter produced during the overlapping period of vegetative and reproductive growth were closely related with the degree of determinancy and earliness; the distribution ratios (%) into vegetative portion were higher in indeterminate and late varieties than in determinate and early ones, and those into reproductive portion indicated the opposite relation with vegetative one. 4. In azuki bean there were little differences in number of leaves and dry weight on main stem among varieties. Varietal differences of total dry matter weight (g/pl.) which were heavier in late varieties resulted mainly in the differences in branches. Main stem ratios (main stem/main stem+branches, %) in dry weight wcre lower in late varieties, especially in viny types. 5. Two peaks of net assimilation rate (NAR) appeared in some varieties of each crop. One occurred at the initial branch-elongation stage in each crop, the other at young pod stage in soybean and at pod filling stage in azuki bean. The patterns of relative growth rate (RGR) were similar to those of NAR, and the peaks were more remarkable in RGR. In kidney bean, values of NAR of indeterminate types decreased rapidly after the flowering. 6. At the initial branch-elongation stage, NAR was corrclated positively, but not significantly, with the distribution ratio of dry matter to leaves (r=0.85) in kidney bean. NAR also indicated positive and significant correlations with the pod growth rate (r=0.83) and the distribution ratio into pod (r=0.95) of main stem at pod filling stage in azuki bean. 7. Grain yield per plant was positively correlated with the growth period, number of node per plant and maximum leaf area. Grain weight per maximum leaf area (g/m²) was, however, lower in indeterminate types than in determinate ones in kidney bean.

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In order to clarify the differences of plant types and their relationships with some morphological characteristics of stem, petiole and leaf, length of petiole, angle of petiole inclination and leaf area of a compound leaf on each node were measured for two varieties in soybean, three varieties in azuki bean and four varieties in kidney bean, grown under the low population density (60cm × 45cm, singling). The results obtained are summarized as follows : 1. Each variety could be grouped into three different plant types according to their mode of the vertical distribution of leaf area. Tokachinagaha (determinate) and Harosoy (indeterminate) in soybean, Maruha No. 1 (late var.) in azuki bean, and Taishoshirokintoki (dwarf), Tokachishirokintoki (determinate, bush) in kidney bean had a greater leaf area distribution towards the top (table type). Takarashozu (early var.) in azuki bean and Kairyo-otebo (indeterminat, viny) in kidney bean had a leaf area distribution which was most abundant in the middle layer and became smaller towards the base and the top (oval type or barrel type). Ofuku (pole type) had a greater leaf area distribution towards the base (triangular type). 2. Angles of petiole inclination changed throughout the growing season in all varieties (examples in soybean are indicated in Fig.2). At the topmost-leaf-expanding stage, there are the specific trends in the vertical distribution of angles (angle of elevation) of petiole inclination; in soybean varieties, number of petioles which showed an upward wider angle increased gradually from the base to the top. In contrast to this, almost all azuki bean and kidney bean varieties except Takarashozu showed the opposite trends with soybean, that is, petioles which had an upward wider angle distributed more in the base than in the top. Takarashozu showed the same mode of distribution at each height. The viny types, Tsurushozu, Tokachishirokintoki and Kairyo-otebo, had more petioles which inclined downward than the non-viny types. 3. There was a highly positive correlation between petiole length and leaf area of a compound leaf on each node. In almost varieties, petiole length and leaf area of a compound leaf are greater on the middle nodes than on the base and the top, but those in Tokachinagaha, determinate type in soybean, became greater towards the top. Thus, the movement of petiole inclination was considered to play the significant role in the vertical distribution of leaf area.

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[in Japanese]

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Experiments were undertaken to test the effects of several environmental factors on the "stunted root" formation in rice plants. The results reported here concern the "stunted root" formation when the plants were subjected to the percolation, the wind, the shading, the heavy nitrogen, and the mechanical stress treatments, respectively. Both the percolation and the wind treatments favorably affected the root growth, leading a decrease in the number of the "stunted roots". On the other hand, the shading, the heavy nitrogen, and the mechanical stress treatments affected unfavorably the root growth, resulting the abundant formation of the "stunted roots", especially in the upper parts of each shoot-unit. The morphological observation of the "stunted roots" thus formed revealed that some of these environmental factors produce their own distinctive patterns of the "stunted roots". Both the percolation and the wind treatments resulted in decreasing the number of "stunted roots" of the deteriolation or the swelling. type; the shading treatment, in increasing that of the tapering type; the heavy nitrogen treatment, in increasing that of the deteriolation, the swelling, or the cessation type, while in decreasing that of the tapering type; and the mechanical stress treatment, in increasing that of the cessation type, respectively. Although the real physiological mechanisms underlying the changes in the external morphology of the "stunted roots" are obscure, yet, these morphological changes may have some diagnostic value in relation to their nutritional and/or toxic effects.

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It had been ascertained by the authors that root hairs of the rice plants were formed in the shorter epidermal cells, and the shorter epidernlal cells were richer in ribonucleic acid (RNA) than longer epidermal cells. But, the study on the root hair formation by observing the fine structure of the epidermal cells, especially cultured at soil condition, has not been conducted. The present work was carricd out to study the root hair formation by observing the fine structure of the epidermal cells of the crown roots cultured under soil condition. The following results were obtained: Generally, the epidermal cells which will be hair forming cells have larger nuclei than those which will not be, particularly at the early stage of the elongation zone. At this stage, authors could not distinguish the root hair forming epidermal cells from the other cells by measuring their cell-length. As regards the fine structures of the epidermal cells, the epidermal cells which will be hair forming cells have more ER (endoplasmic reticulum), mitochondria, and ribosome than those which will not be, when they measured on the same area. These differences were also ascertained at the early stage of the elongation zone of root.

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A few studies on the elongation of root hairs of rice plants in relation to ecological conditions (nitrogen fertilizer, water percolation, etc.) had been carried out by the authors. But the study on the elongation of root hairs in relation to physiological conditions of roots has not been ascertained. The present work was carried out to study the elongation of root hairs in relation to the speed of root growth, root diameter, and thickening of vessel element. The following results were obtained: Generally, at the root apex, papilla bears firstly and then elongation of root hair begins; in this case, at the early stage the growing speed is very slow. Gradually the growing speed of root hairs becomes speedy with time, but at the later stage it decreases and finally stops. As regards the elongation of root hairs in relation to the diameter and the growing speed of the roots, it was found that the thicker roots have longer root apex-papilla distance (i.e. the distance from the root apex excluding root cap to the first papilla), longer root-hair-growing zone and longer root hairs as compared with the thinner roots, and that the roots which grow speedy have longer root hairs than the roots which grow slowly. It was also found that there is close correlation between the elongation of root hairs and the thickening of vessel elements; at the point that papilla were ascertained, matured protoxylem elements (PX) were seen, and at the point that elongation of root hair becomes maximum, matured early metaxylem elements (MXV I) were seen, and at the point that elongation of root hairs stopped, matured late metaxylem elements (MXV II) were observed.

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Isolated "shoot units" each composed of one leaf, one internode and crown roots were cultured using "leaf cutting" method under different conditions in order to investigate the factors influencing the root diameter and elongation. Roots cultured under the leaf-lightened condition marked high elongation rate up to 4-5 cm/day. Root elongation continued for more than 50 days and diameter of their newly elongated parts gradually decreased. Dark treatment as well as defoliation quickly reduced both elongation rate and diameter of roots. Apical parts of roots which continued to elongate for relatively long period became as thin as 200 μm in diameter, but those of roots which stopped quickly were relatively thick (400-500 μm). In shoot units cultured in 0.5-3.0% glucose solution, their roots were thickened and elongated at a high rate (3-4cm/day) even in dark. On the other hand, mannose was severely inhibitory to root development. Ammonium, nitrate or auxins at certain concentrations reduced the elongation of root but they did not have any positive effect on the diameter. Kinetin increased the diameter of roots, but reduced their elongation rate. The results seem to show: 1) among the tested substances, sugar proved to be the most important for root development and 2) for elongation of a root with a certain size of diameter, enough quantity of sugar supply corresponding to its diameter is indispensable.

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[in Japanese]

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Physiological factors associated with the decreasing of lodging resistance of the plants at booting stage due to submersion were discussed. Apparent photosynthetic ability, respiratory ability and the chlorophyll, protein, phosphorus and potassium content of the plant were studied as physiological factors. 1. Under submersion, the apparent photosynthetic rate of the leaf blade, leaf sheath and internode were immediately decreased. 2. The chlorophyll contents of leaf blade were more or less similar in the submerged and the control plants, but those of sheaths of the 14 th and 15 th leaves were higher in the submerged plants. But the same was lesser in all the internodes of submerged plants. 3. The respiratory rate of the leaf blade and sheath was comparatively smaller in the submerged plants than the control ones. But the same was higher in the elongated internodes of submerged plants. 4. The protein content in the leaf blade, leaf sheath and internode, as a whole decreased abruptly in the submerged plants. 5. The soluble phosphorus and potassium content seemed to be unchanged in leaf blade and leaf sheath of the submerged and the control plants. It was, however, in large quantity in the elongated internode of the submerged plants. In the elongated internodes high rate of respiration and cell elongation were observed and these might have resulted due to accumulation of soluble phosphorus and potassium in large quantities.

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Developing process of rice ovary, var. Koshihikari, was observed with microscope by semi-thin sections, prepared through double fixations of glutaraldehyde and osmium tetroxide and embedded in Spurr's resin. 1. The accumulation of starch grains made rapid progress in the endosperm during 8-22 days after flowering, and the accumulation almost finished in each part, the centre in 15 days, the dorsal side in 15-20 days, the ventral side in 20 days, the lateral sides in 20-25 days and the lateral-dorsal sides in 25-30 days after flowering successively. 2. The dorsal vascular bundle fell into deformation about 30 days after flowering. 3. In the nucellar epidermal cells of the dorsal and lateral sides, dense cytoplasm, numerous small vacuoles and fibrous structure (arrows) were observed 6 days after flowering, and subsequently the cytoplasm became dilute or transparent but nucleus and osmiophilic globules on and after 7-10 days. The nucellar epidermis degenerated 20 days after flowering in the ventral side, 25 days in the lateral sides and 30 days in the dorsal side successively. The developing aspects in the nucellar epidermis, as mentioned above, are thought to correspond closely with the accumulating process of starch grains in the endosperm. 4. The nucellus inside the nucellar epidermis was compressed to a thin layer 5 days after flowering, however, the degeneration in the dorsal side continued till 20-25 days and survived four or five layers of the nucellar projection. As the cell walls of the degenerated nucellus are stained purple-blue with toluidine blue O, the walls may easily let solutes pass through. 5. About the time when the proaleurone cells ceased to proliferate 7 days after flowering, started off the accumulation of lipid and the formation of aleurone vacuoles, and the globoids could be found about 14 days after flowering. The aleurone cells had thick walls with no wall-ingrowth, however, stained purple-blue with toluidine blue O. 6. The increase of cell number in the endosperm reached to the end 7 or 8 days after flowering, and as seen in Figs. 6 and 9, each cell of the endosperm had foamy vacuoles and a nucleus in the centre. Thereafter, the foamy structure of vacuoles disappeared as increase of starch grains. 7. It is supposed that, after migrating from the sieve elements of dorsal vascular bundle to the nucellar projection, solutes transfer to the endosperm by two pathways. One is "dorsal pathway" on which the solutes straightly transfer from nucellar projection into endosperm, and the other is "nucellar epidermis pathway" on which the solutes transfer into endosperm via nucellar epidermis.

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Rice endosperm at 4 to 5 days after flowering is presumed to be considerably heterogenous judging from the high frequency of occurerlce of abnormal mitoses and wide variation of nuclear volume. In such endosperm the differences of starch polimerization degree were frequently observed among the cells which were produced simultaneously. By using the endosperm at 3 to 5 days after flowering for investigating this phenomenon, diurnal periodicity of mitosis, nuclear DNA contents and chromosome number of endosperm cells were studied. Diurnal mitotic activities of the endosperm cells of cv. Towada (japonica) from the 3rd to the 4th day after flowering and cv. Century patna (indica) from the 4th to the 5th day after flowering, were examined by the acetocarmine squash techinique. The mitotic frequency was found to increase at 3 or 4, 17, 21 and 23 or 24 o'clock respectively, regardless of cultivar and days after flowering. Two kinds of microspectrophotometric methods, the one spot measuring method and the two wave length one, compared with each other using the intact nuclei which were prepared from homogenate of the endosperm in cv. Aichiasahi (japonica) at 5 days after flowering and stained by Feulgen reaction. DNA content of nucleus determined by the one spot measuring method was about 12 to l5 percent less than that determined by the two wave length method, but the values by the former were stable. So the estimate of nuclear DNA content in this experiment was made by the one spot measuring method with the wave length 550 nm. Relative DNA contents of intact endosperm nuclei varied from 0.4 to 9.1 in cv Aichiasahi at 5 days after flowering. The relative DNA content per nucleus was examined by use of the longisection of caryopsis of cv. Aichiasahi at 5 days after flowering in four zones of endosperm showing in Fig. 1. The comparable and standard values of DNA content were taken by the DNA content of embryo nuclei on the same section. The 2C, 3C, 4C and 5C nuclei were found in each four zones in this stage, though the rice endosperm had a common origin from the triploid fusion nucleus. The frequency of occurence of 3C nuclei was highest in aleuron layer and central zone. While the frequcncy of occurence of 5C nuclei was relatively higher in marginal and middle zones. The ranges in relative DNA contents of nuclei in middle zone were largest, from 0.2 to 9.1. Chromosome number of endosperm cells of cv. Kosen (indica) at 4 and 5 days after flowering was examined by acetocarmine squash techinique. It could not be ascertained whether the endosperm cells were aneuploidy or not, but the approximate values of 1C, 2C, 3C and 4C in chromosome number were obtained. These results mentioned above indicate that the rice endosperm was consisted of heterogenous cells which markedly differed from the DNA contents of nucleus, but these cells were almost systematically distributed from the aleuron layer towards the central zone; polyploidy level rised from aleuron layer via marginal zone to middle zone and declined in the central zone. These polyploidy was presumed to be endopolyploidy which were due to the endomitosis leading to high polyploidy. Some functional significance of endopolyploidy was envisaged with the higher rate of synthetic activity required by the specialized cells of glands, suspensors and endosperms. Therefore it was presumed that the differences of starch polimerization degree among the cells of middle zone which were produced simultaneously, might be caused by high polyploidy and the large variation of polyploidy level among the cells of middle zone.

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