66 
Journal of Agricultural Research 
Vol. V, No. 2 
The remaining five of these seven infected plants were carefully dug 
up, the stems cut off at their junction with the rhizomes, washed very 
clean with a brush, and disinfected in corrosive sublimate for five min¬ 
utes. After this they were planted in steam-sterilized soil in the green¬ 
house, in which there had never been any Plasmopara kalstedii . On 
May 23 two shoots broke through the ground; and three days later, when 
one was 1 inch and the other 2 inches high, they.were covered with jelly 
glasses in order to keep the atmosphere moist. On this date the initial 
leaves appeared chlorotic, but no spores of Plasmopara kalstedii could be 
found. The next day the lower surfaces of the leaves were almost cov¬ 
ered with a glistening white coat of conidiophores and spores, which 
on microscopic examination were found to be the conidia of Plasmopara 
kalstedii. Of the three remaining rhizomes, two failed to come up, while 
the third sent up a spindly shoot on June 5. This shoot was treated in 
the manner already described and the fungus fruited in the same way. 
This experiment showed that the diseased plants grown in the green¬ 
house manifested the same symptoms as those grown in the open. It 
also showed that the mycelium of Plasmopara kalstedii may be present 
in the rhizome of Heliantkus diversicatus , and this, coupled with the obser¬ 
vations described, strongly suggests that Plasmopara kalstedii is peren¬ 
nial in the rhizomes of Heliantkus diversicatus. 
CONCLUSIONS 
As seen from these investigations, several species of the Peronospora- 
ceae live over from one growing season to another by at least two means: 
Resting spores and perennial mycelium. As is well known from the 
excellent studies of De Bary (2), the oospores germinate after a rest 
period either by zoospores or germ tubes and cause the infection of plant 
tissues. Because of their extremely ephemeral nature, the conidia 
hardly merit consideration as resting organs, but, nevertheless, they may 
under certain conditions function as such. If a fungus has two or more 
annual host plants, it may spread to one or more by conidia after pri¬ 
mary infection has resulted from oospores on one; or the fungus may be 
perennial in one host and spread to another by conidia borne on the 
former—e. g., Phytophtkora infestans on the potato and tomato. 
The species of Peronosporaceae known to have perennial mycelium 
are given in Table II. 
