Feb. i2, 1917 
Studies of the Genus Phytophthora 
265 
oospores fall into the classes below 27.5 ijl than into the classes above that 
number. The remaining species have slightly larger oospores. 
The two curves in figures 11 and 12 show the diameter of the 
oospores of the species belonging to the phaseoli group, and, as in the case 
of the curve showing the measurements of the chlamydospores, were 
constructed from the data given in Table III and the classes made to 
differ by 4 instead of 2 ju. It will be seen that the oospores of P. erythro- 
septica have the greatest diameter and that those of P. arecae and P. 
phaseoli follow. The curves of the species of the cactorum group are 
shown in figure 12, but on account of the smaller variation the differ¬ 
ences can not be used to advantage. In the case 
of P. infestans only 150 oospore-like bodies were 
measured. The results of the measurements of 
the diameters of these are shown in text figure 13. 
They varied from 23.5 to 39.5 /x, but most of them 
fell into the classes ranging from 38.5 to 44.5 /x. 
Germination of oospores. —The methods fol¬ 
lowed in obtaining germination of oospores are given 
by the writer in another publication (29). To date 
P. cactorum from Phyllocactus sp., P. cactorum from 
Panax sp., and P. fagi from Fagus sp. have been 
germinated. The process of germination in these 
three forms is the same. After a period of rest 
and under proper conditions the oospore wall takes 
on a striated appearance, and later the striations 
disappear and the wall itself diminishes in thick¬ 
ness. Through a break in the wall a germ tube 
is sent out, and into this a part of the contents 
of the oospore gradually passes. When the tube 
has reached a certain size, it bears one or more 
conidia, and these also may germinate by means 
swarm spores. 
BIOMETRICAL CONSTANTS 
The use of biometry in obtaining biological data has been employed 
since the middle of the nineteenth century, but few biometrical studies 
have been attempted with fungi. On account of their variability, the 
spore forms of the genus Phytophthora offer a good object for such a 
study. 
Pearl (22) says: 
A description which says nothing about the magnitude of the thing described is 
not complete, but on the contrary, lacks an element of primary importance * * * 
it is certain that not only are quantitative methods needed in biology, but also that a 
far more serious need is for something of the methodological viewpoint. 
at or oasrcmr-i/M? 
OUrOFri7P7?% <?r/& 
Fig. 13.— -Graph showing the 
variation in the diameter 
measurements of the oospore¬ 
like bodies of Phytophthora 
infestans. 
of germ tubes or by 
