PERISPORIALES 



195 



prefer damp climates. The only endophytic species, Leveillula taurica, 

 belongs to dry subtropical regions whose phanerogams are generally 

 xerophytes with a very thick epidermis. Further it appears that the 

 Erysiphaceae in the tropics generally only propagate by imperfect forms 

 and that the perithecia degenerate. 



They are also sharply specialized even in their ectophytism (Salmon, 

 1900, 1903; Steiner, 1908; Blumer, 1922; etc.). From the numerous 

 forms so far studied, except for Erysiphe dehor acearum, none is able 

 to go beyond a single host genus, and is often limited to a single species 



Fig. 122. — Leveillula taurica. Conidiophores. ( X 830; after Foex, 1913.) 



or group of species within the genus. Salmon (1904, 1905) has shown, 

 however, that here our observations on the fundamental relationships 

 need clarification. If one wounds old leaves whose cuticle normally 

 resist infection (e.g., if one cuts away a piece of epidermis), the fungus 

 may then infect the mesophyll. In this manner, transitions between 

 various biological strains might be possible. 



As imperfect forms, only conidiophores and conidia are known; 

 earlier pyenia were ascribed to the Erysiphaceae but they have since 

 been demonstrated to be the fructifications of a parasitic imperfect, 

 Cicinnobolus Cesatii. The conidiophores are at first formed on both sides 



