The effects of nitrogen application, shading and soil moisture on the growth and seed production of Bidens pilosa L. var. radiata Scherff., an aggressive perennial sugarcane weed in the Ryukyu Islands, were investigated under laboratory conditions in order to provide physiological and ecological evidences for the effective control of the plant. The results are summarized as follows:
1. The leaf area, number of offshoots and number of capitula increased considerably with increasing nitrogen level. A similar tendency was noted in the main stem length, root weight, T/R ratio, top dry matter weight, achene weight per capitulum and 1, 000 kernel weight. The days to flowering decreased with increasing nitrogen level (Fig. 1-3, Table 1-2).
2. The main stem length, leaf area and T/R ratio increased considerably as the shade intensity was increased. The top dry matter weight showed a similar tendency, while the root weight, number of capitula and top dry matter coefficient decreased considerably. A similar tendency was noted in the number of offshoots, achene weight per capitulum and 1, 000 kernel weight, while the days to flowering increased as the shade intensity was increased (Fig. 4-6, Table 3-4).
3. The T/R ratio and top dry matter coefficient increased with increasing moisture intensity, while the number of offshoots, achene weight per capitulum and 1, 000 kernel weight decreased. The top dry matter weight, root dry matter weight and number of capitula also decreased to a marked degree. The main stem length increased most in the 42% treatment. Flowering took place earlier at higher moisture intensities (Fig. 7-8, Table 4-7).
4. As has been observed, this weed is characterized by the fact that its growth is promoted at higher nitrogen levels, at higher shade intensities and also at lower moisture intensities. It is accordingly concluded that the weed can infest any sugarcane field where nitrogenous fertilizer is used in large quantities, the crop provides sufficient shading and in addition, the soil is less moist. For effective control, it is suggested that the weed should be removed while it is still in its early stage of growth.

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In order to analyse the mechanism of seed propagation in water hyacinth occurring in the southern part of Japan, the formation of capsules and seeds was studied. The results are summarized as follows: 1. Capsule setting percentage through two seasons ranged from 0 to 9% by open pollination, while that by artificial pollination ranged from 0 to 97%, with an average of 56%.
2. Pollen fertility was high in summer, and pollen grains germinated well on the agar medium at 20 to 40°C, with maximum germination at 30°C.
3. The low capsule setting percentage by open pollination was mainly attributable to the fact that the pistils could hardly receive pollen grains under natural conditions.
4. It was considered that self-pollination did not play a significant role because anther dehiscence was not observe before flowering, and only a few pollen grains were dispersed during the flowering period under natural conditions.
5. On the other hand, the probability of pollination by insects also seems quite low, because visit of insects was not observed.

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Inhibition mechanism of pigment biosynthesis by the herbicide glyphosate was analysed using submerged leaf disks prepared from pea plants and the following results were obtained:
(1) Although three kinds of aromatic amino acids were taken up by the plant along with the herbicide they could hardly alleviate the physiological and biochemical changes induced by the glyphosate treatment (Table 1 and Fig. 1).
(2) Addition of precursors of pigment biosynthesis imperfectly alleviated the physiological and biochemical changes induced by the glyposate treatment. However the decrease in the content of chlorophylls and anthraquinones and the abnormal accumulation of shikimic acid in the presence of glyphosate could be alleviated by the addition of three kinds of aromatic amino acids, phosphoenolpyruvate and δ-aminolevulinic acid at the same time (Table 1 and 2).
(3) Methoxyphenone, which inhibited the final step of the biosynthesis of carotenoids, caused an abnormal accumulation of phytoene, phytofluene and ζ-carotene and also decreased the content of β-carotene. Glyphosate did not cause any abnormal accumulation of these compounds but decreased the content of β-carotene. It was thus assumed that the inhibition of carotenoid biosynthesis by the glyphosate treatment did not occur at the final step of this pathway (Table 3).
(4) Incorporation of ¹⁴C-acetyl Co A into each fraction of chlorophyll, carotene and xanthophyll was inhibited to the same extent by the glyphosate treatment (Fig. 2).
(5) It was suggested that, in addition to the inhibition of 5-enolpyruvylshikimic acid-3-phosphate synthase, glyphosate inhibits metabolic sites at the initial stages of the biosynthesis of plant pigments.

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The heading behavior of some Digitaria adscendens Henr. populations collected from Kyushu and Shikoku were examined under field and controlled conditions.
Under natural day length condition, a wide variation in mean heading date, ranging from 17 July to 12 September, was observed among 14 populations sown in the field on 12 June.
Two distinct types of heading behavior were recognized in the populations in a successive sowing experiment and a photoperiodic response experiment, viz, day-neutral type and short-day type. The early-heading population headed independently of the seasonal photoperiodic conditions and of the different photoperiods of 24, 15 and 13 hours. The results indicate that the early-heading population possesses the day-neutral type heading behavior. Headings of the late-heading populations were largely influenced by seasonal photoperiodic conditions and were retarded under the 24 and 15 hour day-lengths, suggesting the presence of photoperiodic thresholds in reproductive initiation. Thus, the late-heading populations were shown to possess the short-day type heading behavior.
Some aspects of population differentiation in heading behavior were discussed.

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This study was conducted to determine the variation of growth and propagule production in the response of 19 clones of Sagittaria trifolia L., collected from six locations in southern Kyoto Prefecture, to four levels of nitrogen application (0, 8, 16 and 32kg/10a). Clonal variation was found in the nitrogen response to plant growth. Both sexual reproduction by achenes and vegetative reproduction by tubers increased with the increase in plant growth. The pattern of increase differed among the clones. The nitrogen response pattern differed according to the characteristics mentioned above. The increasing extent of sexual reproduction was higher than that of the vegetative one.
The relationship between dry weight of the heaviest tuber and the number of tubers per ramet differed extensively among the clones. The nitrogen response of this relationship also differed. Of the 19 clones, 7 increased only in number, while 12 increased in both number and dry weight of the heaviest tuber. Although the heaviest tuber weight differed among the nitrogen levels, except in the case of two clones showing poor growth at 32N, the different nitrogen levels scarcely affected the frequency distribution of tuber weight.
Based on the four characteristics of plant length, achene production, tuber production and the relationship between dry weight of the heaviest tuber and the number of tubers per ramet, the 19 clones were divided into four patterns. Intra-locational variation of these patterns was recognized in three of the six locations examined.

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Tolerance of large crabgrass of different ages and strains to propanil was surveyed, and the absorption of propanil by shoots and its hydrolyzing enzyme activity have also been studied.
There were no great differences in susceptibility to the herbicide among large crabgrass plants from different locations in Japan at the 4th leaf stage. Significant difference in tolerance was found among large crabgrass plants at different ages, as well as barnyardgrass. The younger large crabgrass and barnyardgrass were more susceptible to propanil and tolerance to the herbicide incre ased as the leaf stage increased. Neither species of plant hydrolyzed the substance even at the 6th leaf stage. The concentration of ¹⁴C-radioactivity in large crabgrass at the 3rd leaf stage was much higher than at the 6th.
Large crabgrass was shown tolerant to propanil only at the 6th stage, and differential tolerance to the compound in different strains was not found significant. It was suggested that the mechanism of tolerance of large crabgrass at the 6th leaf stage to propanil was not due to the detoxifying hydrolytic activity of the herbicide, but due primarily to the lower absorption of the compound by the shoots.

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