226 



CLOSED TYPE OF ASCOCARPS 



can be examined without revealing the minute hard black asco- 

 carps (Figs. 149; 152, A). Many of these fungi are quite con- 

 spicuous since the ascocarps are formed in large compact masses 

 and also because they are often associated with a more or less 

 conspicuous outgrowth from the mycelium called the stroma 

 (Figs. 150; 152, D). The majority of the genera are saprophytic 

 upon dead and decaying vegetation, though some of them are 

 destructive parasites. The black knot, Ploivrightia, the cause of 

 a serious disease to plum and cherry trees, illustrates very well 

 the characteristics of this order. The mycelium grows in the 



Fig. 148. Forms of ascocarps found among the powdery mildews: A, 

 Phyllactinia with needle-like appendages enlarged at the base. B, Micro- 

 sphaera, appendages dichotomous at apex. C, Uncinula, appendages coiled 

 at apex. D, Erysiphe without appendages and crushed to show escaping 

 asci. E, an ascus containing six ascospores. 



cambium and cortical regions of the branches, causing the bark 

 to split open in the spring when spore bearing hyphae extend 

 up into the air forming a velvety coating (Fig. 150, c). By the 

 approach of winter, this mycelium has grown into the familiar 

 black knotty mass in which are developed numerous ascocarp- 

 like bodies (Fig. 150, as). The spores from these ascocarps are 

 carried by the wind in the early spring to other branches and 

 probably infect the budding trees. Other conspicuous forms are 



