Perennial Mycelium in Species of Peronosporaceae 67 



There can be no doubt that the myceUum of several species of Perono- 

 sporaceae may become perennial. Of course this can take place only when 

 the host is a winter annual, biennial, or perennial, and quite generally 

 infected. Such plants may live through the winter and renew activity 

 in the spring, when the fungus may sporulate and spread the disease. 



The perennial nature of the mycelium of other species of the genus 

 Phytophthora has not been studied critically, but there is reason to 

 believe that Phytophthora infestans is not the only one that may become 

 perennial. In many cases other species produce oospores prolifically. 

 Butler and Kulkarni (4) believe that on Colocasiae Phytophthora 

 colocasiae may survive the dry seasons of India in the mycelial stage. 

 Another case of perennial mycelium is that of Phytophthora cactorum 

 on ginseng {Panax quinquefolium), a perennial having a fleshy root, 

 described by Rosenbaum (14). The Phytophthora fungus flourishes on 

 the roots, and, according to this author (14), can spread from the roots 

 up the stem to the surface of the soil, and produce conidia which infect 

 the foliage, a case very analogous to Phytophthora infestans. 



Table II shows that, so far as known, only one species of Cystopus has 

 perennial mycelium — that is, Cystopus candidus on two hosts, Lepidium 

 virginicum and Capsella bursa pastoris. Both of these plants may be 

 either annuals or winter annuals, and in both the fungus may become 

 systemic and may survive the winter, provided the host plants live. 

 Unlike Phytophthora infestans, Cystopus candidus produces oospores pro- 



