Feb. 12,1917 
Studies of the Genus Phytophthora 
251 
forms erythroseptica , arecae , and parasitica can be distinguished with 
ease from the remaining forms by the fact the former have a predominat¬ 
ing ratio of more than 1.5 and the latter a predominating ratio of less than 
1.5. Of the three forms having a ratio of more than 1.5, the predomi¬ 
nating ratio of P. parasitica approaches 2, while that of P. erythroseptica 
and P. arecae is less than 1.75. 
Another distinguishing character is the degree of development of the 
papilla of the conidia. Camera-lucida drawings of the papilla of typical 
conidia are shown in text figure 9. The papilla of P. syringae and P. 
erythroseptica are broad and flat and not easily distinguished from the 
curvature of the wall. The papilla of P. faberi are raised and very promi¬ 
nent, while the papilla of the other forms show all gradations between 
Fig. 5.—Graph showing the variation in width of Phytophthora infestans , P. cactorum 
(Phyllocactus sp.), P. erythroseptica . and P. arecae . 
these two extremes. The shape of the papilla is constant under all con¬ 
ditions and therefore a good character for use in taxonomy. 
Germination of the conidia. —In the 10 forms which the writer had 
in culture, the germination of the conidia was studied; and in all it was 
found that germination took place either by germ tube or swarm spores, 
as shown in Plate 75. Potentially each conidium is a sporangium, and, 
as regards the method by which it germinates, it is influenced, in part 
at least, by environment. 
No differences were noted in the germination by means of germ tubes 
of the conidia from various species. The method may be described as 
follows: After the conidium is mature and the papillum formed, one or 
more tubes are produced. These arise from any point of the conidium, 
