Evidences have been confirmed concerning climatic conditions in relation to the severeness of black rot of sweet potatoes in fields. The data were obtained from the variety experiment at Shirai-mura near Chiba from 1941 to 1948.
The basal portion of inoculated slips healed not infrequently after planting, though they used to be attacked there. The healing was distinguished in the year with the highest mean temperature being at about 30°C for 10-day-period. The temperature observations were taken at 10 o'clock. The higher in the temperature the more remarkable is this phenomenon (Fig. 1). This is referred to as the effect of a curing as such mentioned by YOSHII (1945).
The varietal difference of the infection of the roots has a tendency to be correlated with the injury by wire worm, Melanotus caudex LEWIS. Similar tendency is acertained in regard to the yearly deviation on the same varieties (Fig. 2).
The number of the pits was in inverse proportion to the precipitation at the first 10-day period of March (Fig. 3). In this case the correlation coefficient reaches to -0.89 and is highly significant. At about this period, the wire worm in that field is surmised to move upward from deep to just beneath the surface of soil, and subject to the effect of precipitation. Deviation of the dots Nos. 16 and 17 in Fig. 3 is explained by the earlier upward movement resulted by warmer winter (Fig. 4) and larger precipitation of the preceding 10-day period in the year Showa 16 (1941), and by the delayed upward movement caused by colder spring (Fig. 4) and meagre precipitation of succeeding two 10-day periods in the year Showa 17 (1942). The number of the pits may be presumably in proportion to the number of the worm itself. The precipitation of the first 10-day period of March has a curvilio, near relation to the percentage of the diseased roots (Fig. 5), similar to that between the latter and the index of the wire-worm pits.
The length of the lesion at the basal portion of the slips correlates with (1) the mean temperature for the last two 10-day periods of August (Fig. 6). Correlation coefficient reaches to 0.92 and is highly significant. (2) the mean temperature for the growing season of sweetpotato, (3) the mean temperature for September and October, and (4) the mean of maximum temperature for the first two 10-day periods of September also suggest tendencies of positive correlation to the enlargement of the lesion, though it is not significant. As a whole, the higher the temperature in August or thereafter, thel arger is the development of the diseased part at the base of the stem.
This is apparently in contradiction to the result on the healing mentioned first. However, the curve B in the figure 6 suggests a rather suppressive effect of high temperature in 1948 (22 in the figure).
The distribution of the dots in fiure 7 is suggestive of a certain influence of concentration of the pathogen on the outbreak of this disease in the field, since the meagre outbreak of the disease in 1941 (16 in the figure) cannot be explained otherwise, i. e. the lower temperature in summer and autumn might prevent the increase of the pathogen, in spite of the worm pits were rather numerous in this year.

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Rhizopus nigricans EHRB.による甘藷軟腐病と傷部の状態との關係につき試驗を行つた。
軟腐病は傷より發病する。しかし,濕室に貯藏した場合の如く,傷口の細胞が生活力旺盛であればその傷部は生理的に抵抗性があり,又,傷の下に形成される木栓層も防禦の役をする。各種の處理をうけて弱つた傷部は生理的抵抗性,並に傷痍木栓層形成力の減退によつて本病にかゝりやすい。
接種前並に後の貯藏庫の濕度,貯藏日數の軟腐病に對する關係は第2表,第1圖の通りである。この關係の傾向も亦生理的抵抗性及び傷痍木栓層形成力で説明しうる。

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1. As has been reported in the previous paper, the ability of B. solanacearum of utilizing carbohydrates in synthetic media is variable accoding to the kinds of the food material used as a nitrogen source; namely, in the presence of nitrates the organism produces acid and gas from dextrose, saccharose, etc., while in the case of ammonium salts only an acid reaction is noticed. This fermenting ability can therefore be employed as a means of distinguishing the strains. In Formosa there are at least 4 strains, one of which is the tomato strain and the others are tobacco strains. The former is considered to be identical with the SMITH's orginal type and the latter may be the strains derived from the former. These strains can be differentiated by the fermenting ability of dextrose, lactose and mannit, provided that 0.1 per cent solution of K₂HPO₄ and NH₄NO₃ plus agar was used as a basic medium and brom thymol blue as pH indicator.
2. Among the first-named three strains, morphological differences were noticed in the size of individual cells, number of flagella and staining reactions. but under the microscope these were not sufficiently distinct to separate them from one another. In milk cultures the tomato strain clears the milk, shifting the reaction to an alkaline side, while the tobacco strains coagulate the casein by the formation of acid.
3. It is confirmed by a number of isolations made from the diseased tomato and tobacco plants that there exist some relationships between the strains and host plants. The tomato strain is usually highly infectious to tomato plants, though it is also parasitic on tobacco, producing a mild symptom usually confined to the one side of the plant, when they are attacked at a young stage under the moist, hot weather conditions. On the other hand, the tobacco strains are not only virulent to tobacco, but also sometimes attack tomato plants to such an extent as giving the symptoms hardly distinguishable from those produced by the tomato strain. It is noticed, however, that the tomato strain, if allowed to take the long-continued in vivo life on tobaccoes by means of the successive passages or to remain long on the same host without. transfer, was able to change into the tobacco strain-I which is capable of producing the acuteform symptoms on tobacco plants. The tobacco strain II appears to have a character of losing virulence which is acquired by the continuous association with tomatoes.
4. In the previous paper, the writer reported on the relationship between the diphasic symptoms and colony variants, but the results of the present studies conducted by means of rootinoculation revealed no evidence to support it, because the colony variants, C and Op types, which were considered as a cause of mild-type symptom in the field have little abilities to cause a wilt disease, and if they could, the symptoms were very mild, only restricted to some lower leaves which are characterized by a yellowish local withering or blackening of the veins, and not extended to the whole plants. The symptoms of tomatoes affected by the tomato strain are either the mild or the severe types depending upon the condition of the host and weather, while the tobacco strain-I usually gives the severe-type symtoms on tobaccoes, and the strain-II gives the mild one. The latter, however, is able to produce the severe type if the plants is young and succulent, and the weather is hot and humid. It is further noticed that any strains tend to produce the mild-type symptoms after having decreased their virulence. The writer is inclined to believe that the diphasic symptoms may be partly due to the conditions of the host and temperature.

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1. 甘藷モザイツク病葉は健葉に比較して粗剛な觸感を與えるが,病葉は健葉より約1.2～1.9倍剛いようであつた。
2. これらの粗剛さを持つ生理的變化の中,主として肉眼的觀察からその構成樣相を檢討した。病葉脈の構成は病葉の粗剛さを十分に表現するものの一つである。又葉肉の構成も波状不規則であり,水分含有量が多量であることも葉體の彈力に深い關係があるとみられ,葉縁の屈曲性も矢張り彎曲に對する抵抗となる。
3. 病葉の表皮は健葉のそれよりも紫外線による燒斑が輕度であつたが,細胞膜のCutin及びSuberinの反應に著しい差異を認め得なかつた。表皮細胞の形態面積には殆ど關係がないようであつた。

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(1) 長崎縣五島に於て粟に年々被害を起す一種の病害を研究した。
(2) 本病は病徴において,さきに中野勝喜氏によつて發表せられた粟不稔病に一致するも,病原線蟲の形態學的研究を行つた結果,從來之が病原線蟲はTylenchus sp.として取り扱われて來ているが, Aphelenchoides屬に入るべきものなることを明かにし,稻心枯線蟲即ちAphelenchoides oryzae YOKOOとの比較を行い,同一種なることを確めた。

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(1) Cephalothecium菌による抗菌性物質Cephalothecinの生産力に影響を及ぼす培養條件を探索し,併せて該物質の化學的性質を究め,その抽出分離を實施した。
(2) Cephalothecinの生産用培養基としては半量式のRCHARDS合成液が最も優れており,培養基のpHは4-7の範圍が良効であるが, pH5-6でその生産量は最高を示した。
(3) 窒素源としては硝酸態窒素が良い影響を與えるが,特にKNO₃が優れた性質をもつている。アンモニア態窒素は餘り良効な結果は齋さなかつた。炭素源は蔗糖が優り,加用量は2.5%が最良である。葡萄糖は5%前後が良い結果を示した。
(4) 培養添加物としては,玉蜀黍浸出液を容量當0.5%加える事によりCephalothecinの生産力は最高を示した。麥芽浸出液の場合には容量當1-2%加用がよい成績を齋した。
(5) Cedhalothecinは比較的耐熱性の弱い物質で,アルコールに可溶性で,活性炭によく吸着されるが,アセトン,エーテル,クロロホルムにてよく溶出される。中性及び鹽基性醋酸鉛にては殆んど沈澱しない。重曹アルカリ性ではエーテルに移行しないが,硫酸々性にてよくエーテルに移行する。
(6) Cephalothecinは分解點が124-126℃で,ハロゲン,硫黄,窒素及び燐の元素を含まず,炭素,水素及び酸素の3元素にて構成される物質である。

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