Feb. 12,1917 
Studies of the Genus Phytophthora 
271 
The following tentative table is offered for the separation of species: 
A. Cactorum group. —Majority of the oogonia have the antheridium on side. P. 
cactorum , P.fagi , P. syringae , P. nicotianae. 
B. Apical papilla not prominent, but broad and flat. 
C. Mean length of conidia 39.86 ju, mean width 25.33 ju, mode 
for width 26.18 ju, mean diameter of oospore 29.5 
fx .1. P. syringae . 
BB. Apical papilla prominent. 
C. Chlamydospores absent, mode for length of conidia 32 to 
33 jl x, mode for width of conidia 25 to 26 fx. 
D. Mode for diameter of oospores 29.86 mean 
diameter 30.22 v .2. P.fagi . 
DD. Mode for diameter of oospores 26 fi, mean 
diameter 27 ju.-3. P. cactorum. 
CC. Chlamydospores produced abundantly, mode for length of 
conidia 37 to 38 /i, mode for width 29 to 30 /x. 
D. Mode for diameter of chlamydospores 28.86 /x* 
mean diameter 31.15 ju, mean ratio of length to 
width of conidia 1.25.4. P. nicotianae . 
AA. Phaseou group. —Majority of oogonia have the antheridium at the base. 
P. phaseoli , P. erythroseptica , P. arecae, P. parasitica, and P. infestans. 
B. Mean ratio of length to width of conidia greater than 1.75. 
C. Mean length of conidia 43.64 /x, mean width 23.39 ax, mean 
diameter of chlamydospores 31.15 v _5. P. parasitica . 
BB. Mean ratio of length to width of conidia less than 1.75. 
C. Conidia small, mean length less than 30 j u, mean width 
less than 20 ju- 
D. Producing an abundance of oospores on oat agar, 
antheridia present.6. P. phaseoli. 
DD. Oospores or oospore-like bodies lacking or very 
scarce on oat agar and when present having 
antheridia entirely absent or indefinite. 
7. P. infestans . 
CC. Conidia large, mean length more than 30 mean width 
more than 20 m. 
D. Apical papilla not prominent, but broad and flat. 
E. Mean diameter of oospore 35.78 v with a standard 
deviation of 3.77, mode for length of conidia 
47-93 M> mode for width of conidia 26.20 
/x .8 . P. erythroseptica. 
DD. Apical papilla not as above but prominent, mean 
diameter of oospore 32.42 /x with a standard 
deviation of 4.53, mode for length of conidia 
44.65 n, mode for width of conidia 29.45 /x. 
9. P. arecae. 
AAA. Faberi group. —Antheridium entirely unknown or its relation to the oogonium 
not yet determined, chlamydospores absent or present. P. faberi , P. 
jatrophae. 
B. Chlamydospores large, mean diameter more than 35 ax. 
C. Mean diameter of chlamydospores 38.98 /x, mean ratio 
of length to width of conidia 1.47.10. P. faberi. 
BB. Chlamydospores small, mean diameter less than 35 m- 
C. Mean diameter of chlamydospores 32.89 ax, mean ratio of 
length to width of conidia 1.28.11. P. jatrophae. 
