Oospore Wall Research Articles

Germination of Resting Fungal Spores

I HAVE read with interest Mr. Robert McKay's letter1 on the germination of oospores of Peronospora Schleideni. He notes the remarkably persistent oogonial wall, which “forms an additional protective layer” around the oospore, and the still more persistent oospore wall. In germinating these highly resistant spores he lays claim to no special method: in course of time, in this case of years, the spores germinate when placed in water.

THE DEVELOPMENT OF THE SEXUAL ORGANS IN LEPTOLEGNIA CAUDATA

Leptolegnia is one of the less common genera of the Saprolegniaceae and until recently has been represented by only one species, L. caudata deBary. This species was first tentatively placed in Saprolegnia by deBary (I2), but later (I3) he established the genus Leptolegnia based on the one species. The mycelium is typically composed of a circular, whitish fringe of regular threads around a fly or other insect or bit of seed in water. The strains vary considerably in their robustness, the form from Chapel Hill being considerably less robust than those from Long Island or Florida, the threads of the latter often approaching a well developed Saprolegnia in thickness and length. The sporangia, in their thread-like character, resemble those of Aphanomyces, though the behavior of the spores in Leptolegnia is more like that of the spores in Saprolegnia. The otogonium in Leptolegnia shows a superficial resemblance to that of Aphanomyces in that each contains only one egg. The beak-like process on the oogonium, which usually grows out where the antheridia are applied, the exceedingly thick oospore wall, the peculiar eccentric arrangement of the oil globules in the ripe oospore, and the fact that the oospore completely fills the oogonium are characters which make this genus stand out from the other genera of the Saproiegniaceae. The ripe oospore of Pythiopsis cymosa, however, with its lunate cap of oil globules is quite similar to the oospore of Leptolegnia. Although the fungus has been reported from a number of diverse regions its occurrence is rather infrequent. In Europe it has been reported from Germany by deBary (I2, 13), Fischer (I4) and von. Minden (i8); from Denmark by Muller (2I) and Petersen (25); and from Latvia by Apinis (I). In America it was first reported from North Carolina by Coker (7) and has since been collected by Thaxter in New England, by Pieters at Ann Arbor, Michigan, in Florida, and on Long Island, N. Y. (see Coker, 8). It is interesting to note that Petersen (25, P. 5II) and Muller (2I) record the fungus as an exceedingly destructive parasite on Leptodora Kindtii.

Societies and Academies

DUBLIN. Royal Dublin Society, December 16, 1913.—Dr. J. H. Pollok in the chair.—Prof. K. Yendo: Cultivation of sea-weeds in Japan. Sea-weeds are extensively used in Japan as food, glue, and manure. The annual amount of production is estimated at about 800,000l, of which 300,000l worth is exported, chiefly to China. The most important point in cultivation is to give the plant a suitable ground for attachment. Various factors, such as depth, light, salinity, temperature, nature of substratum, movement of water, &c, have great influence in limiting the growth of sea-weeds in a certain locality. The author explains these factors with reference to plant-life in the sea, and describes the modes of cultivation in Japan.—Dr. G. H. Pethybridge: Further observations on Phytophthora erythroseptica, Pethyb., and on the disease produced by it in the potato plant. The peculiar mode of development of the sexual organs (intra-antheridial growth of the oogonial incept) described for this species by the author in a former paper, and shown by him to occur also in P. infestans and P. phaseoli, has been found in P. parasitica, Dast., and P. colocasiae, Racib., by Dastur, and by Butler and Kulkarni respectively. In the present paper the production of zoospores and of germ tubes by the conidia and the mode of germination of the oospores is described for P. erythroseptica. The inner thickened part of the oospore wall is composed of cellulose, and previous to germination becomes dissolved, so that it thus appears to serve not only as a protective covering for the spore, but also as a store of reserve carbohydrate. The fungus with its reproductive organs has now been found in all the underground portions of the potato plant. It is the cause not only of a specific rot of the tubers, but of a disease of the plant as a whole, of the “wilt” type, the outward symptoms of disease being rather similar to those produced by Bacillus melanogenes, Pethyb. and Murphy.—Prof. H. H. Dixon: Note on the spread of morbid changes through plants from branches killed by heat. Experiments are described showing the possibility of washing out the poisonous materials liberated in the water tracts of branches killed by heat, and thus removing the contamination from the water supply of the leaves above. The withering of the leaves on a killed branch may in this way be long postponed. It is also possible to wash back the contaminating substances from the dead branch into other branches, when it is found that the leaves on the otherwise uninjured branches wither. Both these experiments show that it is not allowable to assign the withering to a failure in the water supply brought about directly by the death of the cells of the heated branch.—W. R. G. Atkins: Oxydases and their inhibitors in plant tissues. Part iii., The localisation of oxydases and catalase in some marine algae. Catalase was found in all algae tested. Out of a total ot twenty-nine, only one alga gave the direct oxydase reaction, while six gave the indirect with guaiacum. In two cases only was a colour produced with α-naphthol.—Prof. T. Johnson: Bothrodendron kiltorkense, Haughton, sp.: its cone and Stig-marian stage. The specimen described supplies conclusive evidence that the Stigmarias found in the Kiltorcan quarry are the underground root-carrying rootstocks of Bothrodendron. In one specimen organic continuity is shown between the aërial stem with typical leaf-scars and Stigmaria with apoendages, a horizontal line of demarcation indicating the ground level. The paper also contains a description of a fertile shoot ending by repeated forking in four tips of which three are stalked cones, 3×5 cm. in extent, the fourth being sterile.