The concept of isobole method was investigated and verified to be closely related to the Similar joint action and the Similar synergistic action of BLISS and FINNEY.
For more general application of the isobole method, the acceptable definition of the additive effect was proposed.
Methods for determining the most favorable mixing ratio of two herbicides were described.

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A large number of phosphorothionoamidates, phosphorothionothiolamidates, phosphorothiolamidates and phosphoramidates were synthesized and their herbicidal activities were tested.
This paper deals with structure activity relationship and biological activity of some phosphorothionoamidates.
O-Alkyl-O-(subst'd phenyl) phosphorothionoamidates were high in herbicidal activity. The phosphorothionoamidates having orthonitrophenyl substituted with halogen, lower alkyl and alkoxy at paraposition showed excellent herbicidal activity.
O-Ethyl-O-(2-nitro-p-tolyl)N-isopropyl phosphoramidothionate, common name: amiprophos (supposed) was of the most interest from the points of herbicidal activity and compatability to crops.
Amiprophos did not affect seed germination. It suppressed the growth of germinating shoots and roots as to both crops and weeds. The shoots and roots of treated plants showed abnormal enlargement and “club-shaped” appearance.
The cells of treated plant at the apical meristem were as small and denese as those of untreated plant. Immediately behind this region, however, the cells of treated plants were abnormally large and aberrant.
Amiprophos was highly persistent to rainfall and leaching. And then, it showed high placement selectivity to a number of deep-seeded crops such as rice, maize, beans, radish and carrot, and trans-planted crops such as rice, tomatoes, cucumber, lettuce and onion.

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The behavior in soil of amiprophos (O-ethyl O-(2-nitro-p-tolyl) N-isopropyl phosphoramidothionate) in which we was the most interested from the points of efficacy and selectivity was investigated by gas liquid chromatography using flame photometric detector and ³²P-amiprophos tracer.
Amiprophos was highly persistent in soil surface layer.
The rate of disappearance of amiprophos from soil was affected by soil temperature, texture and microbial metabolism.
According to ³²P-amiprophos tracer technique, four degradation products were found as main products. They were amino amiprophos, amiprophos oxygen analog, O-ethyl N-isopropylamino phosphorothioic acid and O-ethyl phophorothioic acid.
Oxidative and reductive metabolisms would take place simultaneously under paddy condition. Oxidative metabolism would take preference to reductive one under upland condition. In fact, production of the reductive product such as amino amiprophos in upland soil was considerably smaller when compared with that in paddy soil.

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1) Tests were carried out on the rhizome and frond development of field bracken (Pteridium aquilinum (L.) KUHN) and the effects induced by asulam of the rhizome of the plant when the leaves were treated with the compound.
2) The total lenghth of the rhizome segments dug up for one plant was 30m, the rhizome having a diameter of about 1cm and being at a depth of from 7 to 25cm; the main stem of the rhizome was 3.7m long, the average length of the primary branches 1.25m, and of the secondary branches 0.29m.
3) New fronds are visible late in April in the central part of Japan. Growth of the axis appears to slow down during the early part of autumn. At the end of a growing season, the majority of the secondary branches of the rhizome carry one or two frond buds, which may serve to establish new fronds in the next year.
4) About half of the total number of fronds were found to carry an abaxial bud at their bases.
5) The fronds were dead within two months after the leaves of field bracken were treated with asulam and regrowth from the rhizome was prevented.
6) It seemed that asulam was translocated to the growing points of the rhizome branches readily enough to result in rotting within seven days after treatment.
7) The respiration of rhizome decreased soon after foliar treatment with asulam and after two months of treatment the decrease was remarkable.

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1) For the purpose of labor-saving of weeding in the planted forestry of Taiwan, tetrapione (Sodium-2, 2, 3, 3-tetrafluoropropionate) was tested in the forestry of Acacia confusa at Hengchun (Pingtong) and Pahsienshan (Hsinchu) in 1970.
2) Eulalia (Miscanthus sinensis), one of the most troublesome weeds in the forestry of Taiwan was satisfactorily controlled by the application of tetrapione. The optimum rate was approximate 4.5kg a. i. per hectare.
3) Growth of ferns, herbacious broad leaved weeds and shrubs in the tetrapione treated area increased compared with those in the untreated area. However, change of the vegetation due to the application of tetrapione did not give any bad influence on the growth of the planted trees, because those alternated weeds were not tall enough to shade the planted trees.
4) The results obtained in these tests indicated the feasibility of tetrapione in the forestry of Acacia confusa on which tetrapione did not show any symptoms of phytotoxicity.

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Several experiments were conducted to learn the phytotoxicity of simetryne on rice seedlings under different temperature conditions, using several kinds of soils. The result obtained are summarized as follows:
1. All herbicides combined with simetryne provided similarily the increase of rice injury as temperatures rose from 20°C to 32°C on the average when applied at the same rate of simetryne. Strictly speaking, however, a mixture of X 52 (2, 4-dichloro-3′-methoxy-4′-nitrodiphenyl ether) and simetryne seemed to provide to some extent less toxicity on rice under a high temperature. Further, it was found that a mixture of NH 6967 (2, 4-dichlorophenyl pyrrolidine corboxylate) and simetryne gave relatively severer toxicity in each of all temperature conditions, probably due to additive action of both chemicals.
2. Rice injury with simetryne under three different temperperatures was examined using eight different soils. Rice injury undr a high temperature, 32°C on the average, markedly varied with the sorts of soils. The severest was found in Quartz sand, decreasing in the order of river sand, volcanic sandy soil (SHIRASU), paddy clay soil, red-yellow soil derived from marine alluvium, and red-yellow soil derived from shale.
3. Relationship between phytotoxicity with simetryne and some properties of soils was taken into consideration. The correlation coefficients between the index of rice injury and each of clay percent, organic matter percent, and pH in soils were -0.855, +0.124 and +0.591, respectively. It appears that clay content in soils is highestly related to rice injury with simetryne.
4. Another aspect with reference to soil characters is a consideration of clay minerals. Clay soils contained monmorillonite brought lighter injury on rice that contained kaoline minerals, beyond expectation from clay percent in soils.

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Several anatomical characteristics of leaf blade, related to weed control techniques and/or herbicidal activity, have been studied using 23 weed species and 3 crops of rice, wheat, and barley. The results are as follows
1) Based on information already reported by DOWNTON, AKITA, and TAKEDA, whether or not chloro-plasts and starch grains exist in vascular bundle sheath cells (BSC) was examined, and as the result weed species employed in this experiment could be divided into two groups of photosynthesis, i. e. nonchlorophylous C₃ and chlorophylous C₄ plants in the pathways of CO₂ fixation.
2) Out of 26 species used, six species of Panicoideae, three species of Eragrostoideae, two species of Cyperaceae and Portulaca oleracea were considered to belong to the C₄ plant and the other 14 to the C₃ plant. There was a distinct difference in the number and arrangement of vascular bundle between two group plants. The C₄ plant, for instance, has narrower space between neighboring vascular bundles. That accounts for much vascular bundles distributed in the leaf blade of the C₄ plant.
3) It is said that the surface structure of leaf blade is related to adherence of chemicals when applied on foliage. Corrugation Index (b/a) was obtained from measuring lengths of corrugation line (b) and its bottom one (a) in the cross section of leaf blade, as shown in Fig. 2. This index varied considerably with weed species, showing higher values in Gramineae and Cyperaceae than in broadleaved weeds. However, one kind of broadleaved weeds, Marsilea quadrifolia, indicated a higher index as an exception. Out of Gramineae, the highest was found in Leptochloa chinensis. This fact suggests us that this grass weed may not be controlled by the same procedure as barnyardgrass.
4) Thickening of external membrane in epidermis that may be a factor concerning penetration of chemicals into mesophyll has been observed. Thicker membranes were in Gramineae and Cyperaceae than in broadleaved weeds. Further, out of Gramineae species, rice (Oryza sativa), goosegrass (Eleusine indica), and green foxtail (Setaria viridis) have thicker membrane than the others.
5) Air cavity in the mesophyll of leaf blade varied with weed species. Generally speaking, aquatic weeds such as Sagittaria pygmea and Potamogeton distinctus had large cavity, which may make less cell-by-cell migration of chemicals in mesophyll. The cavities of the above two weeds were 50.7 and 34.7 percent of total leaf area on the average, respectively.

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The dormancy of the seed, effect of temperature on the emergence and seedling growth were studied. The results were as follows:
1. Freshly harvested ripened seeds of Common Purslane showed high percentage germination under favorable condition. But, no germination occured under the dark condition and low temperature as 20°C.
2. The optimum temperature for emergence was over 20°C and minimum temperature was 12-13°C.
3. The optimum temperature for growth at early stage was over 20°C and under the temperature the growth was showed little.

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