62 



Journal of Agricultural Research 



Vol. V, No. 2 



Tabi,E I. — Record of six collections of plants of Lepidium vtrginicum infected with 

 Peronospora parasitica 



Date of collection. 



Number of 



plants on 



which fungus 



sporulated. 



Nov. 5. . 

 Dec. 14. 

 Dec. 18. 



Feb. 22. 

 Mar. 6. . 

 Mar. 25. 



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 possibiHty, 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 myceHum 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, 

 191 1, one plant showed white pustules of Cystopus candidus on Decem- 

 ber 17, three days after the plants were collected. The following day 



