oct. H, 1915 Perennial Mycelium in Species of Peronosporaceae 61 
The first collection of plants of Lepidium virginicum , numbering about 
20, was made on November 5, enough soil being taken up with each plant 
to keep the roots from being disturbed. The plants were taken to the 
greenhouse and transplanted in two flats, or shallow boxes, and on 
November 6 each box was covered with a low bell jar to keep the air 
moist, a condition favorable for the sporulation of the fungus. An ex¬ 
amination of the plants next day showed but 2 inactive, the leaves of the 
other 18 being turgid and expanded in the normal way. It also showed 
that 2 of the plants were covered with a white glistening growth, which 
on microscopic examination was found to be the spores and conidiophores 
of Peronospora parasitica. The following day this fungus was found 
sporulating on 3 additional plants, and 8 days after the plants had been 
collected it was found fruiting on some portion of 12 of the 18 living. 
Although kept under observation for 6 weeks, the remaining six plants 
were free from infection, which showed that it did not take place under 
the conditions in which they were held in the greenhouse. 
On December 14 another collection of plants of Lepidium virginicum 
was taken from the patch on the parking near the drive, the soil at that 
time being frozen 6 inches deep. A block of soil on which there were 18 
of the plants was chopped loose and placed in a flat in the greenhouse, 
and after being allowed to thaw out for 24 hotfrs was covered with a glass 
house. On December 17, 3 days after the plants were brought into 
the greenhouse, 1 was nearly covered with conidiophores and spores of 
Peronospora parasitica , the next day 4 more showed fruit of the fungus, 
and at the end of the sixth day an additional plant, or 6 in all, showed 
fruiting of the fungus, indicating that at least that number was infected 
when collected (PI. Ill, fig. 2, A). The fungus fruited on both sides of 
the leaves and also on the new leaves developing from the crown, though 
not as abundantly on these as on the older leaves. 
Besides the collections of November 5 and December 14, 4 others, or 
a total of 102 plants, were brought into the greenhouse from the 2 
patches during the dormant period of the host plant. In the case of 
several of these collections Peronospora parasitica sporulated on some of 
the plants 2 days after their transfer to the greenhouse, but usually the 
disease did not appear before 3 to 5 days and, when the infection was 
weak, not before 8 days after the transfer. Table I gives date of col¬ 
lection, number of plants in each collection, date of first evidence of 
Peronospora, number of days required for the fungus to sporulate, and 
number of plants on which the disease appeared. 
