For the purpose of studying on heading characters in the rice plants genetically, the authors collected 14 mutant strains on heading which were induced from 5 varieties by X-ray or β-ray (cf. table 1), and investigated their characteristics on heading and others, espesially, photoperiodic sensibility and minimum heading duration. The results were as follows: ( 1 ) Generally speaking, the earliness or lateness on heading time of these mutant strains comparing with the original variety wewe mainly attributable to the decreasing or the increasing of the photoperiodic sensibility, and slightly, were connected with the minimum heading duration too, (cf. figs. 1, 2, 3, 4, 5, 6). ( 2 )For further particulars, M₁ strain from Norin-No. 8 was 10 day earlier than the original variety under the natural condition, but was 7 days later under the high temoerature and short day condition. So, in this strain, the photoperiodic sensibility decreased, but the minimum heading duration increased (cf. figs. 1 and 2). The mutant strains which were very early and viridis typwe, i. e. M₃ stain from Norin-No. 8, M₂ strain of Chusei-Aikoku, M₁ strain of Norin-No. 29 were turn into the non-sensible strain on the photoperiodic response on heading time (cf. figs. 1, 2, 3, 4). ( 3 )With some strains, the authors recognized some changes of the morphological and physiological characters, i.e. length of the culm, numger of panicles. siffness of the straw, fetility, etc. (cf. tables 2, 3, 4, 5, 6). (4) It is suggested that these mutant strains may be important and very interesting for the genetical studies on heading time in rice.

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1.This investigation was conducted to clarify the mode of inheritance of cool tolerance in rice, form the view point of its breeding. 2.In this study, the F₁∼F₄ generations from an inter-variety cross ‘Somewake 'X' Aomori No.5' were used. ‘Somewake' is a local variety of high cool tolerance and panicle weight type with color glume and long awn, and ‘Aomori No. 5' is a crossbreeding variety of low cool tolerance and panicle number type without glume color and awn. 3.The degree of cool tolerance was evaluated by sterility of the materials tested in a field irrigated with cool water (14°C). 4.Variance of cool tolerance based on transformed data: Angle=sin^-1√(sterility (%)), was partitioned into D, H and E components according to MATHER's method. Based on these estimates, heritability and the number of effective factors were estimated. 5.Consequently, cool tolerance was supposed to be nearly completely dominant and determined by apolygene system(probably more than 7 effective factors) with an additive dffect. 6.Heritability for cool tolerance was comparatively high even in early generations and a fairly good agreement was obtained with those estimated by other various methods. 7. Linkage relations between one of the effective factors for cool tolerance and the Rp gene which localozed the glume color and between the other one of them and the An gene (one of two awn genes) were recognized respectively.

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With the aim of examining the utility of artificial mutations in plant breebing, several experiments have been conducted since 1956. This paper deals with the radiosensitivity of rice in the X₁ generation and the phenotypic variants appearing in ghe X₂ generation. The varietics used in this experiment were "Aikoku" and "Gimbozu" and two strains (F₇ ) derived from Aikoku X Gembozu, "Wase-ichigata" and "Goku-bansei". The genes responsible for heading period in thcse four starains have been identifled by Syakudo et al. (1954). In the spring of 1956 dry and water-soaked seeds of these strains were irradiated with Co⁶⁰ γ-rays of O.5∼5Okr and the plants from these seeds were grown in the paddy field. In the fall of 1956 10∼20 X₁ plants were selected randomly from each of the varying dosage groups in all the strains, and about three spikes were taken from each of these plants. In 1957 the progenies of these spikes were grown as separate lines, totaling 6888 lines and about 20, OO0 plants. The examination of this X₂ generation was made mainly with Gimbozu. As for the ger, omatomg ability the irradiated seed showed no decline as compared with that of the control even in the highest dose. The seedlings, however, showed a slower growth than the control and in the higher doses some proportion of them were killed in the early stage of growth. The number of plants killed incrcased as the dosage increased, in the highes dose all the plants being perished. Seed fertility of the matured plants decreased lineary as the dpsage incresed until 20 kr, from which the rate of the decrease fell down. The fertility of the plants from water-soaked seed was lower than that of the plants from dry seed at the same dosage. 50% of fertility was obtained in the dosage of 10∼15 kr with dry seed. In the X₂ generation various kinds of mutation were observed. The aberrant plants presumed as mutants are those of chlorophyll defrciency, early and late maturity, tall and dwarf type, dense and lax spike, large-and small-sized or deformed grain, sterility of various degrees and other aberrations (See Table 3). About 30% of these aberrant plants except chloropyll mutants showed simultanious change in two or more characters.

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(1) The vernalized seeds of 16 cultivated barley varieties and 3 wild barley species : i. e., H. spontaneum, H. agriocriocrithon and H. murinum, were grown under different temperatures and photoperiods. (2) The rate of declaying in short day to long day was calculated using the formula (X₂-X₁/X₁) X100 (X₁ : number of days from sowing to flag leaf emergence under long day. X₂ : the same value under short day). This delaying rate differed between varieties but the varietal difference was most remarkable in high temperature-short day condition. (3) The grade of response to temperature under different photoperiods was marked in long day than in short day condition, but varieta. difference was striking in short day than in long day condition. It was caused by the remarkable difference of heading behavior betwveen varieties under high temperature-short day condition. (4) Most varieties headeed earlier in green house than in outdoor, but a few special varieties delayed in green house than in outdoor. In those varieties, the grade of response to temperature took minus value. It was considered that in those varieties, the effect of high temperature at dark period would be more striking than in other varieties. (5) With respect to the absolute earliness, defined as "heading behavior at the condition of high temperature and all day illumination after vernalization", interspecifrc difference was recognized in Hordeum species in which the number of day from sowing to flag leaf emergence ranged from 19.4 in H, spontaneum to 41.0 in H. murinum. In cultivated barley species H. vulgare and wild spccies H. agriocriton, the absolute earliness was distributed between H.spontaneum and H.murinum.

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With an aim to obtain a good source of resistance to leaf-rust of wheats, the amphidiploid of T. Tiopheevi Zhuk, and Ae. umbellulata Zhuk. wassynthesized by treating thc F₁ seed with O.05% colchicine. In the root-tip cells of the F₁ plant, 21 somatic chromosomes were confirmed, which correspone to the sum of the reduced numbers of their parents, and in those of amphidiploids 42 chromnosomes were clearly counted corresponding to the multiple number of chromosomes of the F₁ plant. The modal meiotic configuration of the F₁ hybrid is 1_II+19_I, followed closely by 21_I. Two to four bivalents were observed also. The modal meiotic configuration of the amphidiploids was 21_II, but 20_II +2_I was also encountered rather frequently. The spikes of the new amphidiploid were similar to those of T. Timopheevi, but in the manner of disarticulation of spikes they showed "umbrella-type" dominantly like Ae. umbellulta. The grains were large and firmly adherent to the glumes. They were immune from many races of Puccinia triticia and crossed quite readily not only with the cultivated varieties within uulgare group but also with other species in Dinkel series. Therefore, they are expected to be the useful breeding material as a source of resistance to leaf-rust of wheats.

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Following the previous report (MATSUO and NAKAJIMA 1960), the authors made a study in the gene-analysis of some early heading mutants induced from Norin-No. 8 by X-ray. The materials were as follows: M₁ strain: 1O days earlier than the original variety under the natural condition, but 7 days later under the high temperatire and short day condition. M₂ strain: 40 days earlier; the non-sensible strain of the photoperiodic response on heading, and viridies type. M₄ strain: 20days earlier; the strain decreasing of the photoperiodic sensibility, and the short-culm and stiff-stow type. The F₂ segregations for heading time among the hybrids between original variety and each strain, and between each other strain were investigated. The results were as follows: (1) The earliness of these strains were attributable to the recessive mutation of one gene related to heading time in rice plants (cf. fig. 1 and table 1). (2) These gense which were related to the earliness of each strain were independent from each other (cf. fig. 2 and table 2). Therefore, it was suggested that there were 4 major genes for heading, especially, for photoperiodic sensibility, to say the lease of it. (3) It was evident that the gene related to the photoperiodic sensiblity in M₁ strain had also connection with the minimum heading duaration. The authors suggested that this fact was very important to genetical study of heading in rice plants. (4) Some changes of morphological or physiological characters of these strains, i.e. the sterility of M₂ strain under the short day condition, the stiff-strow type of M₄ strain, were also attributable to the recessive mutation of one gene, and these genes were independent of the genes related to heading time (tables 3, 4).

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The effects of nitrogen, phosphorus and potassium on the so called "spike differentiation " and its development were investigated cyto-histologically, using " Satsukl " a variety of wheat. Sand culture was carried out with several kinds of nutrient solutions. Dr. ISHIZUKA'S culture solution which wvas used for physiological study of wheat plants was adopted as the standard and the following eight plots were provided, (1) PK, (2) 1/4NPK, (3) 3 NPK, (4) NK, (5) N3PK, (6) NP, (7) NP3K and (8) NPK, the control. The developmental process of wheat shoot apex can be devided into three main stages in terms of changes in form and structure. In the first stage the apex elongates gradually and its organization is not so evident. The inception of leaf primordia occurs slowly. In the second stage, the apex extends very rapidly and fundamental structure is established in it. This structure is characterized by the presence of three-layered tunica which mantles less-developed corpus or core. According to SHARMAN'S nomenclature these layers of tunica correspond to dermatogen, hypodermis and subhypodermis. The primordia of upper leaves and bracts initiate rapidly in this stage. In the third stage, the stratified layers of tunica receive some disturbances due to all directional division of cell, and results in the decreasc of the number of tunica layers. On the other hand, the number of cells in corpus becomes to increase becausc of the active all directional cell divisions in it. At this stage the form of apex changes shorter in length and broader in width. The differentiation of spikelct primordia begins in the middle of young spike at first and extends toward basipetal and acropetal directions successively and the apex itself turns to a terminal spikelct finally. Nitrogen, phosphorus and potassium are shown to have some specific effects on each developmental stage. Above all, nitrogen and phosphorus form a strong contrast in their effects. Nitrogen tends to accelerate the progress from the first stage to the second stage, but retards the transition to the third stage, delaying thc period of spikelet primordia differentiation. On the contrary, phosphorus tends to accelerate the transition from the second stage to the third stage and phosphorus deficiency delays the period of spikelet primordia differentiation remarkably. This relation suggests that phosphorus has an important physiological role in the transition from vegetative to reproductive stage in wheat plants. These results are basically the same as those obtained with rice plants.

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In order to make it clearer to understand the varietal difference of the relative flowering period and the relative growing period, and the interrelations to other characters, the effects of daylength on the flowering period and the seed forming period were studied in the experiments of 1953 to 1954. 1. The daylengths from 10 to 18 hours appeared to have greater effect on both of the said periods than on the period to flowering at hours of threshold shorter than the critical daylength. Such an effect differed between the varieties in parallel with the lengths of the periods under short daylength, that is, great on the flowering and the seed forming periods of indeterminate soybeans and the, seed forming periods of determinate large seeded soybeans, while less on both of thc periods of determinate and small seeded soybeans. 2. The difference in the effect of daylength mentioned above was clear between the soybeans of summer soybean type and intermediate type due to the sudden leap of the period at the threshold daylength. 3. Such results seem to make it easy to consider the varietal difference in the relative periods and the interrelations to determinate vs. indeterutinate growth habit and seed size under natural daylength in fields, as shown schematically in Fig. 3.

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1) In this paper, meiotic chromosome pairing and pollen fertility of polyhaploid plants (2n=24) of S.tuberosum (variety Deodara), under two different seasonal conditions, are described in comparison with those of tlle closely allied diploid species S. stenotomum (2n=24 ). 2) The polyhaploids were found to show a frequent occurrence of unpaired chromosomes and an occasional formation of trivalents under unfavorable conditions, in spite of the fact that S.stenotomum had regular meiotic pairing under the same conditions. The pollen fertility of the former plants was extremely low, in contrast witn that of the latter. 3) On the basis of these results, affinity between the two chromosome sets of the polyhaploids is discussed and consequently it is suggested that S. tuberosum can be considered as a segmental allotetraploid.

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