The microscopic investigations were carried out on the morphological difference of external mycelium between the saprophytic and parasitic species of the sooty mould fungi belonging to the Meliolaceae (Perisporiaceae), Capnodiaceae, Microthyriaceae and Deuteromycetes. These results are as follows: 1. In the parasitic species belonging to Meliola, Meliolina, Irene, Irenina, Irenopsis and Amazonia of the Meliolaceae, to Balladyna of the Capnodiaceae, and to Asterina, Parasterina, Lembosia and Morenoella of the Microthyriaceae, the external mycelium is filamentous, straight walled, with hyphopodia or knot cells, and produces reticulate or velvety, small colonies scattering on the surface of the host plants. 2. In the saprophytic species belonging to Capnodium, Neocapnodium, Hypocapnodium, Capnophaeum, Scorias, Chaetoscorias, Chaetothyrium, Aithaloderma, Limacinia, Phaeosaccardinula and Triposporiopsis of the Capnodiaceae, to Perisporina, Dimerium, Dimerina and Phaeostigme of the Meliolaceae, and to Triposporium, Microxyphium and Caldariomyces of the Deuteromycetes, the external mycelium is dematioid, mucilaginous, without hyphopodia or knot cells, and produces membranous or velvety, large colonies covering over the upper surface of the host plants. 3. The presence or the absence of the hyphopodia or knot cells formed on the external mycelium are an important characteristic to distinguish the parasitic from saprophytic species. Almost all of the examined parasitic species have hyphopodia, and rarely knot cells. The hyphopodia are usually definite in shape as well as in arrangement in each species, but in Meliolina octospora these are very few in number, indefinite in arrangement, more or less irregular in shape. 4. The results of histological studies of the host tissue infected with parasitic sooty moulds reveal that nearly all the species produce the penetrating hyphae from the hyphopodia, and that the hyphae send haustoria into the epidermal or rarely subepidermal cells. But some species of the Meliolaceae do not produce the haustoria, and Meliolina octospora produce intercellular hyphae from the hyphopodia, and the hyphae send haustoria into the mesophyll cells. The saprophytic species do not produce the haustoria and also the infection hyphae from the external mycelium. 5. Very similar to powdery mildew fungi in parasitism, the parasitic sooty mould fungi are considered as obligate parasites, and saprophytic ones are considered as obligate saprophytes. These obligate parasites and saprophytes are heterogeneously contained in the Meliolaceae and Capnodiaceae respectively. As regards to the classification of these families from the parasitical point of view, the present author proposes that the obligate parasites having hyphopodia or knot cells on the external mycelium should belong to the Meliolaceae, and that the obligate saprophytes without hyphopodia or knot cells should belong to the Capnodiaceae, and that the Meliolaceae should be divided into the two subfamilies, the Melioleae and Meliolineae, according to the position where haustoria are produced, as the Erysiphaceae is divided into the two subfamilies, the Erysipheae and Phyllactinieae.
In the present paper the writer has treated the taxonomical studies of seven species of Pythium causing damping-off disease of various crop seedlings. The fungi tested are as follows: Pythium aphanidermatum isolated from rotten fruits and from water of the drainage; Pythium deBaryanum isolated from diseased cucumber seedlings; P. vexans isolated from diseased tomato seedlings; P. ultimum isolated from wilted Hibiscus seedlings; P. monospermum isolated from water; P. zingiberum sp. nov. isolated from rotten roots of ginger; and P. Hemmianum sp. nov. isolated from wilted sponge-gourd seedlings (Luffa cylindrica). The sporangium formation is found abundantly in Pythium aphanidermatum and P. monospermum, but not in P. ultimum, P. deBaryanum and P. vexans. It is difficult to make clear the difference between P. ultimum and P. deBaryanum by the characters of sexual organs. In Pythium ultimum, however, one antheridium arising usually from oogonial stalk immediately below the oogonium, attaches to an oogonium, and in Pythium deBaryanum one to three androgenus antheridia attach usually to an oogonium. Butler described that antheridium of Pythium vexans was attached to an oogonium with its broad base. In my observations of P. vexans, such figures were not found, and no sporangium and few conidia were obtained. A new species of Pythium attacking roots of ginger was described as a new species under the name of Pythium zingiberum. It forms numerous oogonia and few conidia on agar culture. Sporangia are filamentous or irregularly inflated and are rarely formed. The oospore wall is smooth and usually filling the oogonium. Antheridia are usually diclinous, and wrap around the oogonium with antheridial branches. A Pythium isolated from wilted sponge-gourd seedlings was also studied. It forms no sporangia and only a few sexual organs, but numerous conidia are formed. The writer gave the name of Pythium Hemmianum to the present fungus as a new species in memory of the sixty first birthday of Dr. Takewo HEMMI.
Toyama Agricultural Experiment Station reported that it was very effective for control of Sclerotinia rot of Chinese milk vetch (Astragalus sinicus L.) to mow the tops of the vetch in autumn. The writer made field tests to confirm the result. When the top of vetch plants was cut off with scissors and the plant fragments were carefully romoved from the plots, the number of affected plants was less, giving higher yield, than the untreated plots. But when the top of vetch was mowed with mower or specially designed sickle, the development of the disease was as much or more severe, as compared with the check. The explanation is that the cutting fragments remained in the plots may serve as a nourishing substratum for the fungus, which become vigorous enough to pass over to the vetch plants.