252 
Journal of Agricultural Research 
Vol. VIII, No. 7 
but most generally near the apex of the spore. The contents of the 
conidium becomes less dense as a result of passing partly into the grow¬ 
ing germ tubes. At the apex the germ tube usually rises from the side 
of the spore a short 
distance below the 
papillum, but sel¬ 
dom from the pa¬ 
pillum itself, and in 
the case of many of 
these germinations 
it is very charac- 
teristicf or the germ 
tubes to arise in a 
whorl or cluster 
near the papillum. 
As the tubes grow 
branches are 
formed. 
Swarm-spore 
germination is 
common not only 
to species of Phy- 
tophthora, but to 
some other mem¬ 
bers of the Pero- 
nosporineae. De¬ 
tailed differences on which separation of genera in this group were 
based are supposed to exist. Speaking of the Peronosporineae, 
Butler (4) says: 
Fig. 6.—Graph showing the variation in width of Phytophthora parasitica, P, 
syringae, P, cactorum (Panax sp.), and P. nicotianae . 
a 
The genus Pythium is separated 
from all the rest by liberating its 
zoospores in an imperfectly differ¬ 
entiated state into a bladder at the 
mouth of the sporange, in which dif¬ 
ferentiation is completed. There 
are other minor differences, such as 
the aerial habitat and parasitism of 
the Peronosporacea, the formation of 
haustoria correlative with the latter, 
etc. None of these differences are 
absolute. 
6 ’ 
Fig. 7.—Diagrammatic illustration showing that the ratio 
of the long to the short diameter of ellipsoidal and spher¬ 
ical bodies offers a quantitative means for designating 
their shape. 
In the study of swarm-spore 
germination in the genus Phy- 
tophthorait was found that at least some of the species liberate their zoo¬ 
spore mass into a bladder or vesicle similar to that described for Pythium 
palmivorum (Butler, 5). This shows a still greater relationship to Pythium 
