Seeds of common purslane (Portulaca oleracea L.) were tested in light and dark germination bed at 30°C, 7, 28, and 100 days after harvest. The seeds were collected from plants which had been planted under several different conditions concerning soil moisture and light intensities. Germination percentage of the the seeds was determined twenty days after laying them in the germination bed.
1. The average germination percentage of eight plants showed no clear difference when the plants had been grown under different soil moisture conditions. Clear difference, however, was seen among the seeds from plants grown under different light intensities.
2. Germination percentage of the seeds showed an increase in time after harvest when the plant was grown under moist soil condition. Except for the seeds from the plants grown under natural light condition without any shading, this tendency was not observed among those from the plants given the light intensity treatment.
3. Variation in the germination percentage among individual plants was greater when they were grown under the condition with excessive moisture. The variation was smaller in other three conditions. With the light intensity treatment, variation in the germination percentage was slightly greater among the plants grown under natural light compared to others.
4. Variation in the germination percentage of the seeds among individual plants grown under excessive soil moisture or under natural light intensity was increased more greatly in dark germination than in light germination.
It was assumed that the germination percentage of the seeds harvested from the plants grown under stressed condition with excessive moisture or with natural light intensity showed polymorphism of the seed with respect to the environmental adaptation.

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The weed communities in sown grasslands were examined on the foot of the Mt. Fuji and the Amagi highland in Shizuoka Prefecture.
1. Weeds, the most frequently observed in the district were Polygonum longisetum, Plantago asiatica, Rumex obtusifolius, Digitaria adscendens, Echinochloa crus-galli and Duchesnea chrysantha.
2. The weed communities on sown grasslands in Shizuoka Prefecture were classified as follows:
I. Poa annua-community group (Differential species; Poa annua, Digitaria violascens and Paspalum thunbergii)
a. Mosla dianthera-community (Differential species; Mosla dianthera and Setaria glauca)
b. Elsholtzia ciliata-community (Differential species; Elsholtzia ciliata and Polygonum thunbergii)
c. Echinochloa crus-galli-community (Differential species; Echinochloa crus-galli)
d. Typical community
e. Rumex obtusifolius-commuity (Differenial species; Rumex obtusifolius)
f. Juncus tenuis-community (Differential species; Juncus tenuis)
g. Juncus effusus var. decipiens-community (Differential species; Juncus effusus var. decipiens)
h. Sasa tuboiana-community (Differential species; Sasa tuboiana)
II. Stellaria aquatica-community group (Differential species; Stellaria aquatica, Setaria glauca, Amaranthus lividus, Acalypha australis and Solanum photeinocarpum)
a. Amaranthus patulus-community (Differential species; Galinsoga ciliata, Amaranthus patulus and Justicia procumbens var. leucantha)
b. Solanun photeinocarpum-community (Differential species; Solanum photeinocarpum)
c. Typical community
d. Phalaris arundinacea-community group (Differential species; Phalaris arundinacea)
e. Duchesnea chrysantha-community (Differential species; Duchesnea chrysantha)
f. Kyringa brevifolia var. leiolepis-community (Differential species; Kyringa brevifolia var. leiolepis)
g. Viola verecunda-community (Differential species; Viola verecunda, Stellaria media, Sagina japonica, Juncus tenuis and Polygonum cuspidatum)
h. Pennisetum alopecuroides-community (Differential species; Pennisetum alopeculoides, Kalimeria pinnatifids and Artemisia princeps)
i. Miscanthus sinensis-community (Differential species; Miscanthus sinensis)
III. Erigeron Sumatrensis-community group (Differential species; Erigeron sumatrensis, Erigeron canadensis, Lapsana humilis, Paederia scandens and Justicia procumbens var. leucantha)
a. Arthraxon hispidus-community (Differential speices; Arthraxon hispidus)
b. Crassocephalum crepidioides-community (Differential species; Crassocephalum crepidioides, Erechitites hieracifolia and Oxalis corniculata)
c. Miscanthus sinensis-community (Differential species; Miscanthus sinensis, Weigela decora and Amphicarpaea edgeworthii var. japonica)
3. Poa annua-community group distributes higher than 800m above sea level, and Stellaria aquatica-community group appears between 450 to 850m, while, Erigeron sumatrensis-community group distributes only lower than 450m above sea level.
4. The dynamics of weed communities in the sown grasslands were presented with a diagram in relation to degree of succession, pasture management and site factor (soil moisture contents).

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The authors have investigated how the perennial weed community changed in the paddy fields, which had been cultivated at different times during stubble field period, that is, at the beginning of August, at the end of August and at the middle of September in 1978, 1979 and 1980 respectively.
The results obtained can be summarized as follows:
(1) In the first cropping season after cultivation in 1979, amounts of emerged Scirpus juncoides Roxb. sp. and Cyperus serotinus Rottb. were less in the cultivated plots than in the non-cultivated ones. The earlier the time of cultivation was, the more the amount of emerged Scirpus juncoides Roxb. sp. decreased.
(2) In the second and the last cropping seasons, the amount of emerged perennial weeds in the paddy fields, which were cultivated during stubble field period, were decreased as compared with the non-cultivated field. In the paddy fields which were cultivated at the beginning and at the end of August, the weed community was dominated by Sagittaria pygmaea Miq. mixed with Cyperus serotinus Rottb. and Eleocharis acicularis Roem. In the paddy field cultivated at the middle of September, the weed community was not only dominated by Scirpus juncoides Roxb. sp. but also by Sagittaria pygmaea Miq. and Eleocharis acicularis Roem.
(3) It was considered that the difference in the amount of emerged perennial weeds and the characteristic transition in weed community were caused mainly by the inhibition of the formation of the multiplication organs of weeds, which resulted from soil mixing by cultivation.
Such variations as above mentioned were under the great influence of the fact that the process of the formation of the multiplication organs at each time of cultivation was different from the weed species.
(4) It was more effective for the inhibition of emergence of Scirpus juncoides Roxb. sp. and Cyperus serotinus Rottb. to cultivate paddy field as early as possible during stubble field period in the early season rice culture in the warm region. But for the inhibition of emergence of Sagittaria pygmaea Miq. it was not so effective that another suitable method should be investigated hereafter.

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This study was conducted to investigate how the emergence of perennial weeds changed, when the different kind of succeeding crops, that is, soybean, buckwheat and Italian ryegrass, were planted at the proper timer espectively, and moreover when the ridging method for the soybean cropping on drained paddy field was changed.
The results obtained can be summarized as follows:
(1) In the first cropping season of paddy rice, 1979, emergence of Scirpus juncoides Roxb. sp. and Cyperus serotinus Rottb. were decreased in each cultivated plot on drained paddy field as compared with the non-cultivated plot. Decrease in the emergence of Scirpus juncoides Roxb. sp. was larger in the early cultivated plot than the late cultivated plot.
(2) As a result of planting the succeeding crops on the stubbled field after the harvest of early season paddy rice, the emergence of perennial weeds in the paddy field was different from the kind of succeding crops.
Such difference as above mentioned was similar to that in case of the time of cultivation which had been reported in the previous report.
(3) It was recognized that the emergence of Cyperus serotinus Rottb. and Eleocharis acicularis Roem. was decreased in the field which was planted with succeeding crops as compared with the field which was only cultivated without croppings.
It was considered that the formation of the multiplication organs was decreased by the reduction in the solar radiation under succeeding crop canopy, and by the inhibition of the regeneration of weeds due to weeding on the border around the paddy field.
(4) For the influence of different ridging methods in the soybean cultivation, emergence of Cyperus sertionus Rottb. decreased in the high ridge plot as compared with that in the level row plot, and emergence of Sagittaria pygmaea Miq. decreased together.
It was considered that the content of soil moisture was lower in the high ridged plot than that in the level row plot, so that the previous tubers were perished and at the same time the formation of new tubers was inhibited.
(5) In the early season rice culture, these kind of succeeding crops after the harvest of paddy rice and the ridging methods for these crops influenced remarkably the change in the perennial weed community.
In order to conduct the weed control effectively, such methods as above mentioned should be applied on the systematic weed control.

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The regrowth ability and behavior of carbohydrates in the subterranean parts of purple nutsedge after shoot cutting were investigated in different light conditions and different growing periods.
In 40-day periods, the tuber formation was slightly depressed by twice cuttings at 13-day intervals. Starch content in the parent tubers of shoot-cut plants was found to be lower as compared with that of untreated plants. This was probably due to the consumption for shoot regrowth from the tubers after cutting. On the other hand, the higher levels of free sugars such as glucose, fructose and sucrose were detected in the parent tubers of shoot-cut plants.
In 120-day periods, although the nmuber of tubers and the tuber weight as well as the starch and sugar contents decreased by cuttings, especially by four times cutting at 24-day intervals, the tuber formation could not be depressed completely.
Shoot emergence in shaded and dark conditions was strongly inhibited after seven times and three times cutting, respectively while in unshaded condition the shoot regrowth and the tuber formation were observed even in the nine times cutting at seven-day intervals.

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Effects of material of seed bed, depth of seed in bed, soil water content, and alternating temperature on the germination and emergence of seed of S. juncoides Roxb. var. ohwianus T. Koyama were studied.
There were no signficant defference of germination percentage among the submerged bed of fine quartz sand, fine glass ball, and soil, and among the depth of 0, 5, 10, 20, 30, 50, 100mm in bed. And all these plots showed the germination of 80-90%. The emergence depth of seeds were 10mm under the fine quartz sand, 30mm under the fine glass ball, 20-30mm under the soil.
Both buried seeds in the submerged soil and in fine glass ball in the field germinated to 80-90% in shallow place of 0-20mm and 7-13% in the depth of 50-15mm. When seeds were buried in soil of different water content, the germination percentage in high water content (field capacity of 70% or more) was greater than in low (field capacity of 60% or less) water content.
The germination percentage at 12/12h alternating temperature of 22-32°C was significantly higher than at 12/12h alternating temperature of 25.5-28.5°C.

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A subspecies of Paspalum distichum L. “Chikugo-suzumenohie” which is distinguished from “Kisyu-suzumenohie” by chromozome number (2n=40), lager plant size and hairy leaf sheath, has increased recently in the creeks of Chikugo area. At present its scientific name is not designated.
Distribution of Chikugo-suzumenohie in creeks in Chikugo area was investigated in relation to the structure and water quality of creeks.
1. Growing area of Chikugo-suzumenohie was 370ha and its occurring percentage to all creeks was 31%. There was a big difference in the covering amount with Chikugo-suzumenohie among regions and creeks.
2. Covering amount with Chikugo-suzumenohie was different from the structure of creeks and the concentration of nutrient of water. It seemed that the higher the NH₄-N or P₂O₅ concentration were in creek water, the more Chikugo-suzumenohie covered creeks. And the more vigorous Zizania latifolia Turcz. or Phragmites communis Trin. grew in the edge of creeks, the less it occurred.
3. The dissolved oxygen level in creek water was remarkably low where the creeks were densely covered with Chikugo-suzumenohie.

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