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The heading response of rice plants to daylength, temperature and nitrogen level was analysed under controlled environments in phytotron. 1. The heading response of rice plants (japonica) to temperature depended on daylength, and on the other hand, the response to daylength depended on temperature. The photo-sensitivity became duller under high temperature and more conspicuous under low temperature condition. These results indicated that the expression of thermo- and photo-sensitivity in heading response of a certain strain may vary with alternative conditions. 2. Nitrogen levels of culture medium did not influence on the growth duration from sowing to heading. No interaction was observed between nitrogen level and temperature or daylength in the heading response. 3. Under short day condition the sensitivity to temperature did not differ between early and late strains. But that of late strains was affected more strongly than early ones under long day condition. The heading of early strains was not affected by daylength under high temperature but affected slightly by daylength under low temperature. The heading of late strains was affected by daylength under high temperature, while it was more affected by daylength under low temperature than under high temperature. 4.These results may suggest that the rice plants in high latitudes have been lowered in the heading responsibility to daylength and growth temperature at several steps of the breeding Process

Flax plants (var. Saginaw No. 1) were grown in pots under conditions of combinations of various day-lengths as follows: transfer from natural day (14h : 20m-14h : 40m) to short day (8h : 00m) was conducted at the third week (CS1 plot), the fourth week (CS2 plot), and the fifth week (CS3 plot) after germination. The control plot grown in the natural day (C plot) and also the one grown in the short day (S plot) were provided. The results obtained are summarized as follows : 1) In the case of the flax plants which were transferred from the long natural day to the short day, the effects of the short day were not recognized in both the date of anthesis and growth of the basal branches from dicotyledonal axilla, on account of the after effects of long natural day during 3∼5 weeks after germination; though the date of anthesis was delayed and basal branches of the plant became larger in the short day than in the long natural day. 2) In the case of the plants which were transferred from the long natural day to the short day at the later time during the 3∼5 weeks, the after effects of the long natural day were recognized in the growth of length of the plants, the contents of crude fibers in dry stems, the diameter of the fiber-cells and the contents of crude-cellulose, but in the case of the plants which were transferred to the short day at the earlier time during these weeks, the after effects were not recognized. These values in the short day plot became smaller than those of the long natural day, while in the case of the plants which were transferred to the short day at the earlier time, these values became just the same as those of the plants of the short day plot. 3) In the case of the plants which were transferred from the long natural day to the short day, the effects of the short day were recognized in the dry weight of the bolls, the diameter of the fiber-cells and the contents of lignin. The dry weight of the bolls and the diameter of the fiber-cells in the short day plot became smaller than those of the long natural day, while in the case of the plants which were transferred to the short day at the later time these values became smaller than those of the plants of the long natural day. The contents of lignin became larger in the plants of both the short day plot and the plots transferred from the long natural day to the short day than in the plants of the long natural day. 4) Growth in the diameter of the stems, the dry weight of the above-ground parts and the contents of α-cellulose in the flax plants which were transferred from the long natural day to the short day became smaller than those grown in the long natural day. These facts seem to depend upon the decrease of photosynthetic products owing to the transfer to the short day, because in the short day the hours of the sunshine per day were shorter than in the long natural day.

In 1957 two varieties of rice plant (Rikuu No. 132 and Norin No. 8) were grown under the condition of long day until they were treated with ten cycles of short photoperiod at the age of eight main-stem leaves or later at the age of ten or twelve ones. Before or after the treatment of short day ammonium sulfate was applied. The plants were exposed again to the long day after the treatment. For comparison, plants were grown continuously under the long day. For the condition of long day the natural daylight was supplemented by the illumination of 40 lux or so for three hours in the midnight. In the relatively insensitive variety to the short day "Rikuu No. 132", there was no difference in the floral initiation and the time of heading between the plant of high nitrogen level given ten photoinductive cycles in the younger age and the plant under the long day. On the other hand the plant of low nitrogen level was induced photoperiodically to the extent as the floral initiation was accelerated and the time of heading was seven days earlier compared with that of high nitrogen level. In the relatively sensitive variety to the short day "Norin No. 8", the floral initiation and the time of heading of the plant of high nitrogen level during the treatment of short day in the younger age were delayed also, compared with those of the plant of low nitrogen, but were earlier than those of the plant under the long day. In the plants of high nitrogen level some main stems could not bring about heading and some others produced deformed ears. Moreover, most of these plants formed a few misshapen leaves in tillers. Such a deformity was the same as the one found by YOSHIDA, one of the authors, in his studies on the photoperiodic after-effect in the rice plant exposed to the long day after insufficient treatment of only several photoinductive cycles. Therefore, it is certain that in these plants the inhibition of photoperiodic induction was brought about. Inhibition of photoperiodic induction in the plant of high nitrogen level during the treatment of short day in the older age was decreased in the variety Rikuu No. 132 and it was uncertain in the variety Norin No. 8.

In order to investigate the effect of temperature on leaf production and transformation of photosynthetic product into various organs, the studies were carried out under both controlled environmental conditions and natural field condition. Obtained results are as follows: 1) Even without clipping, under higher temperature conditions, the growth of various organs decreases gradually, plants become weaker before long, and presents the symptom of summer depression. 2) The higher the temperature, the more the flower buds are formed, and the less the portion occupied by storage organs. And the preparations to regrowth become worse. 3) Becoming worse of preparations to regrowth under higher temperature conditions seems to be a result caused by adaptation to keep the balance between production and consumption. And as a result, the plants make their non-photosynthetic parts less relatively. 4) Maximum leaf-size is found under 15°C and 20°C temperature conditions, and it is found that under higher or lower than this optimum conditions leaf-size becomes smaller. 5) Not only the interval of leaflet emrgence but also that of its death become shorter under higher temperature, longer under lower temperature, but the increasing rate of living leaf number shown by the ratio of the former and the latter reaches maximum at 20°C and 25°C, and becomes less at 15°C and 30°C in accordance with this order. 6) It is found that the number of branches and its increasing rate reach maximum under 15°C and 20°C, and under hither or lower than this optimum conditions they become less. Flower bud initiation is subject to stimulation by long day and high temperature conditions. 7) The higher the temperature, the shorter the number of days required to expand leaflet fully. 8) Judging from the above stated facts, the apparence that total leaf area of the plant under higher temperature conditions may be attributed to the following facts; (1) the size of leaflet under higher temperature conditions is smaller than that of under lower temperature, and (2) lower increasing rate of branches and higher initiating rate of flower bud under higher temperature conditions make the increasing rate of living leaf number less.

In order to clarify the varietal differences in photoperiodic responses of rush plants, tests were conducted from October 1964 to June of the next year. The results are summarized as follows: 1. The sods of clone of four rush varieties (Hirokei No. 373, Sazanami, Asanagi and Hirokei No. 369) were planted in pots on October 1, 1964 and grown outdoors. The plants were moved to each place under three different conditions (long day -natural temperature condition, natural day length -high temperature condition, and long day- high temperature condition) almost every month during the period from October 1964 to April of the next year, and the plants placed under the natural day length- natural temperature condition was tested. 2. Under the natural day length-natural temperature condition, four varieties flowered earlier in order of Hirokei No. 373, Sazanami, Asanagi and Hirokei No. 369, and it was observed that the earlier flowering varieties had a tendency to bear a larger number of inflorescences. As to the number of inflorescences, the same tendency was observed also in cases of plants grown under other conditions. 3. Under the long day-natural temperature condition, the flowering of four varieties was accelerted compared to that under the natural day length- natural temperature condition, in case where the treatments were begun from October or November. The degree of acceleration was higher in order of Hirokei No. 373 > Sazanami > Asanagi·Hirokei No. 369, that is to say, varietal differences in floral responses were observed in the acceleration by long day. 4. Under the long day- high temperature condition, the flowering of three varieties except Hirokei No. 369 was accelerated, even if the treatment might be started at whatever time. 5. Under the natural day length-high temperature condition, the flowering of Hirokei No. 373 was accelerated by the treatments in and after January. The flowering acceleration of Sazanami and Asanagi was observed by the treatments in and after February and March, respectively. From the facts stated above, it is inferred that the critical photoperiods of Hirokei No. 373, Sazanami, Asanagi and Hirokei No. 369 touch a level of about 10, 11, and 12 hours, respectively, i.e., varietal differences in critical photoperiodic responses were observed cleary in case of rush plants.

The present paper contains the reports on the author's experiments which were carried out from 1931 to 1934, in order to know the photoperiodic responses of wheat and barley, with special reference to the physiological distinctions between the spring and winter varieties. On Nov. 2, 1931, seeds of each two varieties of wheat and barley were sown in pots, and plants of these varieties at various stages of their growth were brought under the lengthened light period (24-hour day) for different lengths of time. In one of the wheat varieties and in both of the barley varieties, a long light period at the earlier stage of developm nt was found to retard the transition of the vegetative growth stage to the reproductive one, whileas at the later stage, the development was accelerated under the same long-day condition. In the next year 85 varieties of wheat and barley were sown in pots and immediately after their emergence, they were grown under 24-hour day for a month. An interesting fact observed was that the plants in which the development was retarded, were all of winter types amounting to 35 per cent in number of the varieties investigated. At the later stage, however, they were all forced into the reproductive stage under the same daily light condition. Therefore, when they were grown under the long daily light period continuously from emergence until heading, the hastening effect was less marked than in the case when they were brought under the long day about a month later. In the spring varieties, however, the development was accelerated at every stage. The fact that the photoperiodic response in the winter varieties is less pronounced than that in the spring ones, may be attributed to the cancelling action of the two contrary effects of the long light period at the earlier and the later stages of growth. On Apr. 6, 1932, seeds of wheat variety Akagawa'aka, a typical winter one were sown in pots and during the first 20 and 40 days after emergence they were grown under different day-length conditions. The plant with 8-hour day for the first 20 days came into heading on July 29, and the plant with the same short daily light period for 40 days headed a week earlier than the former, while both the control plant and the one with 24-hour illumination for these days, failed to head. It may be therefore concluded, that the failure by spring sowing of winter cereals to head may be attributed to the excessive length of daylight period for their seedling growth. The extent to which the wheat and barley plants can produce heads normally by delaying the date of spring sowing, differs for different varieties ; the spring types having the capacity to head even in the latest sowing, whereas the winter ones failing in the earlier one. Between these two extreme types there are many intermediate ones as to the extent or the limit of capacity in normal production of head by spring sowing ; i. e. there are many grades of spring sowing habit between a typical spring and an extreme winter types. In order to complete the plant development most rapidly, the optimum day length for the young seedlings of these cereals is different for different varieties. According to the results of the spring sowing experiment with 17 wheat varieties of various grades, it was 8-hours for the winter types, 24-hours for the spring ones and the natural length of day (ca. 13 hours) for the intermediate ones. In the older stage of development, however, the long daily light period forced the plant into the reproductive stage without regard to the grades of spring habit. Ther esults of the experiment in which each two varieties of wheat and barley were sown in the fa'l of 1931, showed that the short daily light period at the earlier stage of growth has no appreciable effect on the development of plants. However, four or five months after emergence, there was found a stage that was especially responsive to the retarding effect of the short day length. It can be concluded, from

Flax plants (var. Saginow No. 1) were grown in pots under different day length (8. 12, 14.and 16 hours). The length of the plants became longer in long days, and the flowering was promoted by the long days. However, in the short day the growth of the plant was restrained and the flowering was delayed. The number and growth of the basal branch sprouted from dicotyledonal axile increased in the short day. The long day condition increased the yield of the fibers and enlarged the diameter of the fiber cells, but the cell wall thickness of the fiber cells became larger in the plants cultivated in short day such as 8 hours. The fibers of better quality were obtained in the short day, for their fibers contained larger quantity of α-cellulose than those in the long days such as 12, 14, or 16 hours. However, in the short day such as 8 hours the lignin contents became larger than those in the longer day length plots.

Several substances contained in the rye diffusate have been continously collected by the method of continous paper electrophoresis. The seeds of annual meadow grass (Poa annua L.) were sown on the top of agar block partially soaked in each fraction, adjusting the pH from 3.5 to ca. 6. The seedlings grown on the agar block were transplanted into the plastic pot later, and were placed under the long day condition. The plants treated with the fractions of 2∼3 and 6∼7 flowered earlier than the control. The number of leaf were also few in those plants. Almost similar results were obtained in this experiment, comparing with the data reported previously.

1. A comparative study of photoperiodic sensitivity of principal rice varieties was made by means of short-day vs. long-day treatments of the plants. 2. Of the 40 varieties tested, naturally earlier maturing varieties were found, in general, to be more sensitive to the treatments, while the medium and the later ones were less sensitive ; the result just agreed with those hitherto obtained by many previous investigators. 3. On the other hand, however, some of the varieties showed different tendencies. 4. According to the types of response observed in our experimentation, the varieties may be classified into following three groups: 1) A group sensitive to both short-day and long-day conditions, 2) A group more sensitive to short-day, but less to long-day conditions, 3) A group less sensitive to short-day, but more to long-day conditions. 5. Generally speaking, with a few exceptions, the earlier and the medium varieties proved to be more sensitive to long day, but less sensitive to short day, while the later varieties were more sensitive to the short day but less to long day.

It is evident in soybean plants that as the intensity of supplemental illumination at night for the purpose of gibing long day decreases lower, the inhibition of blooming due to long-day condition decreases as well. On the contrary, the intensity of the illumination increases higher, the inhibition of blooming increases as well. Furthermore this relation seems to be found more prominently in late-maturing varieties than early maturing ones, even when the supplemental illumination is not so strong. In discussing the influence of day-length, importance of the intensity of light must not be disregarded.

We have investigated by using the same materials as these of previous report the relation between day length temperature and heading time of those rice varieties that are principal in every towns and villages sampled in 1951. Aaccording to many studies, we may explain the result of this research as follows. Generally, when basic vegetative grown is completed, rice plant turned into ear differentiating stage. But this differentiation is to be contorolled by day-length and temperature ; differentiation is inhibited under certain degree of long day-length or low temperature in this stage, and range of inhibiting day-length and temperature differs with varities. In practical culture, we expect rice plant not only to sprout ear, but also to bring good harvest. Therefor the suitable variety and season are choosen against contorol of long day and low temperature. When we calculated the length of the shortest intervals between transplanting and heading, all varieties, from the earliest one-Norin 20 to the latest one Zuiho, show 50∼75 days. We consider the minimum quantity of growth for normal yield may be achieved within these days

1. Number of days from sowing th flowering date of soybean plants showing varietal difference was shortened at a little over 4%∼27% under the comparatively warm night temperature and by the hotbed culture of seedlings compared with each control. In these experiments, the acceleration ratio of flowering under the comparatively warm temperature differs from that of hotbed culture of seedlings. 2. Flowering of 6 varieties was elongated and 2 shortened. But any influence could not be seen in other 2 varieties. While its period under the comparatively warm night was enlarged for all varieties at the different degree. 3. Flowering of soybeans under the short day was accelerated as compared with that of control and the acceleration ratio gradually increased with going to late varieties. Flowering of soybeans under the long day was retarded and the degree was increased generally with going to late varieties. Any flower did not bloom in Morse especially under the long day. Flowering period of Morse was enlarged by the short day, but its period of other varieties was shortened. 4. Flowering was far greatly accelerated by the short day treatment than the warm temperature treatment. The acceleration ratio by the warm temperature treatment has any relation to the late or early habit of varieties. While the response for light is thought to be strengthened with going to late varieties.