262 
Journal of Agricultural Research 
Vol. VIII, No. 7 
time, however, the oogonial thread reaches the top of the antheridium, and curving 
around its apex begins to swell into the oogonium, which by this time is usually cut 
off from its basal thread by a septum. 
It was Pethybridge (24) who showed that the method of fertilization 
suggested by Clinton as possibly taking place in P. phaseoli actually did 
occur in P. erythroseptica . Dastur (10), working independently, showed 
that it also occurred in P. parasitica. It has since been noted by Butler 
and Kulkarni (6) in P. colocasiae , and Rosenbaum (28) has shown that 
P. arecae agrees with P. erythroseptica in this respect. So unique is this 
method of fertilization and the manner of formation of the antheridium 
and oogonium in the fungi that the details have not been worked out. 
Murphy (21), working with Pethybridge and later independently, has 
shown that a branch destined to become the oogonium grows through 
the antheridium and forms the oogonium after it emerges. Plate 76, F, 
shows several stages of this process in P. phaseoli. The antheridium 
continues to clasp permanently the stalk of the oogonium. According to 
Murphy (19), fertilization takes place when 
a tube is pushed in from the antheridium through that part of the stalk of the 
oogonium which lies within the male organ, and through it a single male nucleus and 
the greater part of the cytoplasm passes in. 
Following fertilization, the usual changes, which finally result in the 
oospore, take place. 
In examining species belonging to the cactorum group a condition of 
the sexual organs similar to that found in the phaseoli group, which is 
brought about when the antheridium is superimposed on the stalk 
bearing the oogonium, is sometimes seen. This condition in P. cactorum 
is strikingly similar to that generally found in P. arecae and P. phaseoli , 
but is rare in the cactorum group. 
Following the discovery of this unusual method of fertilization in some 
of the species of Phytopthora, Pethybridge (24) proposed the separation 
of the genus into two genera, the generic name Phytophthora to be 
retained for the group here designated as the phaseoli group, and “Noze- 
mia,” a new generic name, for the “cactorum group.” In reviewing the 
genus, Wilson (37) suggested that if a new genus is to be established the 
name “Pleophytophthora,” for reasons of priority, should be substi¬ 
tuted for “Nozemia.” 
It does not seem to the writer that the genus Phytophthora should 
be subdivided into two genera at present, since both the genus Phytoph¬ 
thora and the genus Pythium, which are closely related, need to be 
investigated further. One of the main differences which has heretofore 
been supposed to exist between Phytophthora and Pythium is the 
production in the latter of a sacklike structure into which the swarm 
spores enter before being liberated. However, it has now been found 
that this structure is produced in several species of Phytophthora also; 
