56 
Mycologia 
antheridium has reached its full size, or almost so, before the 
oogonium appears. At the time of the maturity of the oogonium 
the protoplasm assumes the form of an oospore and withdraws 
a little from the thin-walled oogonium, which at the same time 
becomes thicker walled, and develops a yellowish color. The 
oogonium measures 18-27^ in diameter and the oospores are 15- 
20 /x, with a thick, smooth, hyaline epispore. 
A very interesting portion of the paper is that which deals with 
the chemical composition of the cell walls, which appears to be 
the only published account of such studies on a species of 
Phytoplithora. It has been stated by previous writers that the 
cell-walls of the Peronosporales are composed of cellulose only 
in part, a substance designated callose being present and under 
certain conditions entirely replacing the cellulose. The tests 
failed entirely to show the presence of callose in the cell-walls 
either of the hyphae or the conidia of P. parasitica. The only 
exception to the pure cellulose reaction of the membranes being 
in the oogonium and oospore where the inner walls are of a 
modified cellulose, while the outer walls appear to be of some 
pectic substance. 
The pathogenic nature of the fungus was established by ample 
experiments. Observations were made which proved conclu- 
sively that healthy seedlings planted in the soil in which infected 
plants had grown within a few weeks past were attacked by the 
fungus. This is the first time that a species of Phytoplithora has 
been positively shown to be able to live in the soil for even a short 
time although some of them have been strongly suspected of this 
habit. 
Extensive cross-inoculation work with numerous hosts was 
carried out. Negative results were obtained on cacao, Cereus, 
Colocasia, Clcome, Jasminum , Lepidium, Opuntia, Panax, 
Phaseolus, and tobacco. Slight or indecisive infections were pro- 
duced on Areca nuts and lilac. The following were well infected 
and frequently killed, Clarkia, Fagopyrum, Gilia, Oenothera, 
Salpiglossis, Schizanthus, Solanum Melongena, S. Lycopersicum 
and S. tuberosum. In a field where sesame was grown following 
castor beans the previous year the stray castor seedlings were 
attacked by the fungus and later a species of Phytoplithora indis- 
