DEVELOPMENT OF PLANTS 239 



89. Order d. Sphaeriales or Black Fungi. — ^This is the largest 

 group of the ascomycetes, over 2,000 species being known in the 

 United States alone. Scarcely a fallen twig or bit of old wood 

 can be examined without revealing the minute ascocarps which 



Fig. 147. The stroma of Cordyceps emerging from the pupa of a moth 

 and forming a club-like organ with numerous ascocarps, as, in its apical 

 region. 



more commonly are hard and black in contradistinction to the 

 Hypocreales (Figs. 148; 151, A). Many of these fungi are quite 

 conspicuous since the ascocarps are formed in large compact 

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

 less conspicuous stroma (Figs. 149; 151, D). The majority of 

 the genera are saprophytic upon dead and decaying vegetation, 

 though some of them are destructive parasites. The black knot, 

 Plowrightia, the cause of a serious disease to plum and cherry 

 trees, illustrates very well the characteristics of this order. The 

 mycelium grows in the 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. 149, c). By the approach of winter, this mycelium has 

 grown into the familiar black knotty mass in which are de- 

 veloped numerous ascocarp-like bodies (Fig. 150). The spores 

 from these ascocarps are carried by the wind in the early spring 

 to other branches and probably infest the budding trees. Other 

 conspicuous forms are Xylaria and DaldiniU, which develop an 

 extensive stroma on stumps and trees that contains numerous 

 ascocarps (Fig. 151). In Hypoxylon, the stroma containing the 



