Oct. II, 191S 



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 hours was covered with a glass 

 house. On December 17, 3 days after the plants were brought into 

 the greenhouse, i 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. 



