An investigation was made on the relation among plant type, growth habit and yield in some air-cured tobacco bred lines. High yield air-cured lines were developed from a cross between Shiroenshu, a commercial air-cured variety in Japan, and Burley 49, and from a cross among Shiroenshu. LA burle)" 21 and Coker 254. These lines had high productivity and varied in plant type. These plant types were classified as follows : PT 1 was a pyramidal plant t.vpe, ancl had larger leaves at lower parts of stalk, and smaller leaves at higher stalk position than Shiroenshu. PT 2 was similar in apperance to Shiroenshu. PT 3 was a cylindrical plant type having erected leaves, and its upper leaves were larger than those of Shiroenshu. PT 4 was a large cylindrical plant type, and had larger leaves at whole parts of stalk than Shiroenshu. The growth rate of PT I and PT 2 was high at the early growing stage, and then decreased in PT 1, but PT 2 kept high growth rate to the micldle growing stage. PT 3 and PT 4 were slow in early growth, but in the middle growing stage they grew more rapidly than the former two.

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This research was undertaken to explain why high stomatal frequency (low stomatal resistance) Ieaf had high photosynthetic capacity by gas diffusion theory. Mesophyll resistance was estimated by electrical analogues taking account of respiration during photosynthesis. The mesophyll resistance was estimated from the data of photosynthesis and transpiration in barley differing in stomatal frequency or stomatal resistance. The assumptions were that C0₂ concentration in the atmosphere, C0₂ concentration at the chloroplasts and mesophyll resistance were constant. The results showed that mesophyll resistance was much smaller than was reported previously and stomatal resistance had an important role in controlling photosynthesis.

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The physio-genetical studies on cold tolerance in rice plants were studied. Three paddy rice cultivars Reimei, Kinmaze and Te-tep were used, the former two of which belong to japonica type, and the latter to indica type. At the meiotic stage of pollen development, cold treatment (10-15'C, 4 clays) was performed to induce the abnormalities in anthers and pollens of these cultivars. There were distinct varietal differences in seed fertility. Reimei was the most tolerant to the cold treatment. Close relationship between the seed fertility and the number of dehisced anthers per spikelet was observed, particularly in Kinmaze and Te-tep. Cold injuries such as sterility of pollens, deformance of anther tissue, growth inhibition of anther loculi were observed in all cultivars, although the degrees of these abnormalities varied consiclerably among the cultivars. Anther abnormalities were most frequently observed in Kinmaze. Percent of fertile pollens decreased with the increase of anther abnormalities, particularly in Te-tep. Anatomical observations in injured anthers showed following features : (1) smaller and/ or flattened loculi, (2) tapetal hypertrophv , (3) poor and/or no development of dehiscence -sites, etc. It was concluded from these observations that the occurrence of anther and pollen abnormalities 1were the cause of seed sterility, and the varietal difference in so called "cold tolerance" in rice plants means the grade of resistance of pollen and anther tissue to the low temperature during the meiotic period of pollen development.

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All the meiotic irregularities found in pollen mother cells in cultivated taxa of Came-llia with hybrid heterozygosity as the major cause of genetic unbalance are probably responsible for some portion of the production of abortive pollen in Camellia. Unusual cytological patterns are, in this case, found more frequently in intersectional, interspe-cific hybrids, particularly in hybrids between different ploid levels and high-ploid taxa.

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Genic analysis for heading time was conducted in six crosses of rice involving two Japanese representatlve varleties "Koshihikari" and "Shiranui" by the ald of the close linkage with blast resistance. Koshihikari is a leading rice variety that has been grown in the wide area of the temperate region of Japan since the release in 1956, due to its excellent eating quality and earliness. A late maturing variety Shiranui was released in 1964 for the growing in the Kyushu area of Southern Japan. These two varieties are frequently used as the genetic source of quality and yield in the present rice breeding programs in Ja pan. Two lines, an early maturing "ER" and a late maturing "LR", were used as testers for the genic analysis of heading time. ER and LR were developed from a cross between a Malaysian variety "Morak Sepilai" and a Japanese "Fujisaka 5" by four-time backcrosses of Fujisaka 5 as a recurrent parent. They have the Pi-z^t gene for blast resistance derived from Morak Sepilai. These two lines were selected from a single plant of BC₄F₁ and have a plant type similar to Fujisak-a 5 except for the late maturity of the LR line. The Pi-z^t gene is linked to the heading locus Lm with 2. 4% of recombination in the linkage group I (YOKOO and FUJIMAKI 1971). LR carries a late allele of the Lm locus, while ER has an early allele and heads at the same time as Fujisaka 5.

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Cytogenetical studies on allotriploids, sativa(4x)-punctata[AAB], sativa(4x)-inter-mediate form[AAC] and sativa(4x)-officilealis [AAC] were carried out. At MI of all allo-triploids used in this experirnent, except PF₁ 26 failing in chromosome pairing, 12II+12I were mostly observed. The univalents observed at MI of PMC_S in PF₁ 26 rnay result from a gene or genes which cause disturbance in the pairing of the homologous chromosomes.

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A histochemical observation of changes in starch was performed on the ovules of Petunia hybrida Vilm. which were sampled on the different days from one-day before anthesis to 7-day after anthesis in nature, and which were cultured for 4 days started from 3-day after pollination. For purpose of information, ovules of tobacco were obser-ved on the different days from the day of anthesis to 4-day after anthesis. The obser-vation was performed on the section of the ovules treated with periodic acid Schiff reaction, iodine-potassium iodize reaction or hematoxylin. The most rernarkable finding was the accumlation of starch in the integument of ovules immediately after fertilization. In the point of starch accumulation of the cultured ovules, the normal growing ovule differed from the degenerated ovule. Integumentary tapetum was irregularly hypertrophy in the ovule which contained a abnormal tissue in embryo sac. Owing to the above observation and the fact that the ile vitro development of zygote soon after fertilization was successfully obtained, provided the osmotic value of mediLl.m had been favourable, it is considered that starch accumulation in the integument was related with osmotic value in ovule. The present information shows that the responses of integument which surrounds embryo and endosperm must be paid attention to in ovule culture. Successful ovule culture may be led by devising ile vitro condition by which the integument may be sup-ported such as under nature.

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A total of 74 interspecific reciprocal crosses was made among ten polyploid species of Avena. The development of hybrid kernels was very variable, and grouped into four types, Rd -, Rd +, D + and E - which indicate small or very small, small, mormal and empty, shrivelled kernels, respectively, as vvell as germination (+) and non-germination (-) of hybrid kernels. In a small number of crosses, however, some intermediate types of kernels were found. The results are almost completely explained in terms of a hypothesls of polar-nuclei activation by the male nucleus in double fertilization. The strength of activating stimulus of the male nucleus and reaction of the female nucleus is expressed by terms "activating value (AV)" and "response value (RV)", respectively. Activating values assigned to Avena species show a range from 0.4 to 3 where 1 to A. strigosa is standard. The degree of seed failure is closely related to the differenec between activatlng and response value which usually is represented by an activation index (AI) of the polar nuclei. The AI is c, omputed from a formula, AV/2 RV (or X100%), In a plant selfed the AI is 1/2=0.5 (or 50%), being a normal index, and resultlng in production of normal seeds. If AI deviates from 50% the development of endosperm is often arrested, and it causes the seed abortlon in the extreme case. In the present hybridizations the activation index varies greatly from 7 to 375%Expressing in round numbers less than 20, ₉0-30, 30-80 and more than 80% activation indexes show Rd -, Rd +, D + and E - type kernels, res-pectively. Those of intermediate-type kernels are always found on boundary zones between the four groups. In other ¥vords, it is shortly stated that interspecific crosses of Avena are only compatible when their activation indexes fall within a range from 20 to 80 % .Thus the triple fusion of the two pdlar nuclei with the male nucleus In angiosperms seems to be a sexual isolation mec.hanism and the most efffective barrier to interspecific hybridizations.

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