270 
Journal of Agricultural Research 
Vol. VIII, No. 7 
The difference between the pairs P. arecae and P. erythroseptica and 
P. syringae and P. cactorum may or may not be due to random sampling. 
As regards width, P. nicotinae and P. jatrophae , P. parasitica and P. 
arecae , P. parasitica and P. erythroseptica , and P. infestans and P. 
erythroseptica are certainly different; differences which may or may not 
be significant are found between P. infestans and P. phaseoli , and P. 
arecae and P. erythroseptica; and finally the differences between P. 
cactorum from Panax sp. and P. cactorum from Phyllocactus sp., P. fagi 
and P. cactorum y and P. syringae and P. cactorum are of no value. 
A study of Table VIII shows the differences in the means of the 
oospores of the various species to be significant and also confirms the 
identity of P. cactorum from Panax sp. and from Phyllocactus sp. The 
differences in the mean diameter of the chlamydospores, as given in 
this table, are likewise significant. 
IDENTIFICATION AND SYSTEMATIC SEPARATION OF SPECIES 
In determining a species belonging to the genus Phvtophthora, which 
was one of the objects of this study, the following points should be 
noted, and it is suggested that as many of these as possible be used in 
the descriptions: 
(1) Relation of antheridium to oogonium, whether basal or side. 
(2) Shape of terminal papilla and their relation to the curvature of 
the body. 
(3) Measurements of length and width of conidia, and the diameter 
of chlamydospores and oospores (at least 200 individuals should be 
measured). 
(4) Arrangement of these measurements into classes and determina¬ 
tion of the various biometrical constants. 
(5) Calculations of the mean length and width of conidia and mean 
diameter of chlamydospores and oospores. 
(6) Ratios of length to width of conidia measured and arrangement 
of these into classes, showing the mode. 
(7) Mean, as determined from ratios of length and width. 
(8) Character of conidiophores. 
(9) Germination of conidia, character of swarm spore, etc. 
(10) Growth on various media at room temperature, and noting 
macroscopic appearance and spore forms produced at the end of two and 
six weeks. 
(11) Miscellaneous, such as peculiarities in mycelium. 
It should be borne in mind that no definite criteria are known for the 
identification of species of some of the genera closely related to Phytoph- 
thora, among which may be mentioned Pythium, Pythiacystis, Perono- 
spora, Plasmopara, and Sclerospora. Until further studies have been 
made, however, the above points can be employed to good advantage 
in identifying the species of these genera also. 
