62 
Journal of Agricultural Research 
Vol. V, No. a 
Table I .—Record of six collections of plants of Lepidium virginicum infected with 
Peronospora parasitica 
Date of collection. 
Number of 
plants. 
Date of 
sporulation. 
Number of 
days required 
for sporu¬ 
lation. 
Number of 
plants on 
which fungus 
sporulated. 
1911. 
Nov. 5. 
20 
Nov. 8 
3 
12 
Dec. 14. 
18 
Dec. 17 
3 
6 
Dec. 18... 
12 
Dec. 20 
2 
1912. 
Feb. 22. 
II 
Feb. 27 
5 
6 
1 
Mar. 6... 
24 
Mar. 10 
4 
7 
Mar. 25. 
17 
Mar. 27 
2 
9 
As shown by Table I, 41 plants, or about 40 per cent of the collections, 
were infected before their transfer to the greenhouse. 
It might be supposed that oospores produced the previous year were in 
the soil immediately around and adhering to the plants collected and that 
when warmed up in the greenhouse these germinated and produced the 
infections noted. To test this possibility, 25 leaves were collected from 
the plants in the two patches, washed very thoroughly in running water, 
and placed in a moist chamber, while 25 other leaves were collected from 
the same plants, and without being washed were placed under similar 
conditions as controls. In both cases the fungus sporulated after three 
days, and, although much less than when the leaves were on the plant, 
the sporulation produced sufficient conidiophores to be plainly visible 
to the naked eye, a growth which could probably not be produced by 
oospores. 
Besides this evidence that Peronospora parasitica renews itself by means 
of mycelium as well as oospores, the writer failed to germinate oospores 
after repeated attempts. He has also shown (11) that Peronospora 
parasitica on Lepidium virginicum can be collected at any time during 
the winter and early spring, brought into the greenhouse, and made to 
fruit. Moreover, there can be no doubt that the sporulation on the plant 
collections at Madison was due to living mycelium in the host tissue. 
CYSTOPUS CANDIDUS 
Lepidium virginicum is attacked not only by Peronospora parasitica but 
also by Cystopus candidus , a fungus which can undoubtedly propagate 
itself from year to year by mycelium remaining dormant in the living host 
tissues through the winter. As is well known, these two fungi often 
infect a plant simultaneously, as was the case of some of the plants from 
the parking near the drive. In the collections made on December 14, 
1911, one plant showed white pustules of Cystopus candidus on Decem¬ 
ber 17, three days after the plants were collected. The following day 
