Feb. 12,1917 
Studies of the Genus Phytophthora 
263 
and this, together with other characters, shows a very close relationship 
between these two genera. What constitutes a character of generic 
importance is, in the main, relative. It is of paramount importance 
that further study be made of the species belonging to Phytophthora 
and Pythium before new genera are established in these closely related 
groups. 
SEXUAE BODIES OF P. INFESTANS 
The question as to whether P. infestans produced oospores caused 
much discussion in earlier writings, and among some pathologists and 
mycologists the feeling that this question is not entirely solved still 
exists^ A brief explanation of the statements regarding the oospore¬ 
like bodies of this species previously made in this paper will not be 
out of place here. 
Among the number of strains of P. infestans which the writer grew 
on oat agar in the fall of 1912 one showed a noticeable number of 
brown, more or less globose bodies, which had every appearance of those 
described by Clinton (8) as the oospores of P. infestans . These differed 
from the oospores of the other species grown by the writer in that the 
antheridium was entirely absent in about 95 per cent of the cases examined, 
the remaining 5 per cent showing attachments which might or might 
not have been antheridia. These bodies were preserved in permanent 
mounts, and the many investigators to whom they were Shown agreed 
that they were similar to the bodies described by Clinton and Pethy- 
bridge. The writer made diligent search for these bodies in transfers 
from several of the test tubes in which they appeared in 1912 and in 
other strains of this fungus, but without success until the fall of 1915, 
when he resorted to the following procedure: 
Inoculations were made on the tops of healthy potato plants with cul¬ 
tures made from the strain of the fungus which originally produced oospores 
in culture in 1912. After infection took place and a crop of conidia 
was produced, the conidia were germinated and inoculations again made 
on potato foliage. In this way there were four separate inoculations and 
the culture was kept on the potato foliage for approximately a month. 
Following the last inoculation, the conidia were removed and placed in a 
small flask of sterilized water, which was kept at a temperature favorable 
for germination by means of swarm spores. When an abundance of these 
spores were produced, they were sprayed with a disinfected atomizer on raw 
potato blocks cut under sterile conditions, and within three days these 
blocks were covered with a heavy growth of the fungus. A large number 
of plantings were made from these to oat agar by means of a platinum 
needle. The first transfers were not free from bacteria, but by carefully 
watching the cultures and transferring at the proper time to other oat- 
agar slants a culture free from bacteria was finally obtained. On Septem¬ 
ber 8, transfers from the culture which had recently been growing on 
74550°—17-3 
