Feb. i2,1917 
Studies of the Genus P zytophthora 
273 
tatively, group themselves about a predominating ratio of 2, while those 
of P. nicotianae are found at 1.2 (fig. 8). Similarly the ratios of the 
conidia of all the remaining species vary from 1 plus to 2 plus (fig. 8). 
(11) The degree of development of the papillum is a good character to 
be employed in taxonomic work (fig. 9). 
(12) In their germination of conidia by means of swarm spores at 
least some of the species of Phytophthora liberate their zoospore mass 
into a bladder or vesicle, thus showing a greater relationship to Pythium 
spp. than had been suspected (PL 75). 
(13) Certain species of Phytophthora produce chlamydospores either 
terminally or intercalarily. 
(14) The measurements of the chlamydospores can be used to good 
advantage in delineating species. A sufficiently large number should be 
measured, as in the case of the conidia. 
(15) The relation of the antheridium to the oogonium—that is, whether 
produced at the base or on a side—can be used in separating the genus 
into groups. 
(16) An additional group (faberi group), analogous to the Fungi 
Imperfecti group and embracing forms in which the antheridia are 
absent or their relation to the oogonium yet unknown, is tentatively 
established. 
(17) In one of the several strains of P. infestans , oospore-like bodies, 
resembling those observed by other investigators, were produced, but 
antheridia were absent or, if present, were of a doubtful nature. 
(18) As in the case of conidia and chlamydospores, a sufficiently 
large number of measurements of the oospores should be made if the 
measurements are to be used in identifying a species. 
(19) On account of the variability in the size of the spore forms 
belonging to the genus, a more ready comparison can be made by the 
use of biometrical constants than by a mass of individual measurements, 
and such biometrical constants were calculated and arranged into tables. 
By the use of these constants the identity and relationship of the species 
are further confirmed. 
(20) There being no known criteria for the separation and identifica¬ 
tion of species in closely related genera, such as Pythium, Pythiacystis, 
Peronospora, Plasmopara, and Sclerospora, most of the points enumer¬ 
ated in this paper can be employed to good advantage for this purpose 
in connection with these genera. 
(21) A tentative table, employing some of the above characters for the 
separation of the species, is given on page 271. 
LITERATURE CITED 
(1) Bary, Anton de. 
1876. Researches into the nature of the potato-fungus Phytophthora infestans. 
In Jour. Roy. Agr. Soc., England, s. 2, v. 12, p. 239-269, 8 fig. Reprinted 
in Jour. Bot. [London], v. 14 (n. s. v. 5), no. 160, p. 105-126; no. 161, 
p. 149-154. 
