252 



THE FUNGI 



The fruiting surface of the ascocarps is 

 sometimes very extensive, and is thrown 

 up into irregular lobes and ridges. 



268. The knot and wart fungi. This 

 large group contains forms with peculiar 

 hard black or brown wart and scab-like 

 fructifications, which are found on the bark 

 of trees. Most of the species are sapro- 

 phytic, but some, as the 

 black knot (Fig. 223), on 

 the plum and cherry, are 

 very destructive parasites. 

 The outer parts of the sac 

 fruits contain immense 

 numbers of small cavities 

 (perithecia) that are lined 



Thft convoluted upper with asci - Vei T little is 



portion is an exposed known of the development 



fruiting surface PI i < , 



of such complex sac fruits, 

 but it is probable that many of these fungi 

 are sexually degenerate, as are some of the 

 cup fungi. Xylaria, with its large finger-like 

 fructifications, belongs to this group. 



269. Other sac fungi. Several exceptional 

 sac fungi deserve special mention. 



Ergot. Ergot grains (Fig. 224, A) are hard FlG 223 The black 

 black structures found in heads of barley, 

 rye, wheat, and certain grasses, notably the 

 wild rice. They are really the mummified 



FIG. 222. The morel 

 (Morchella), an edi- 

 ble sac fungus 



knot (Plowrightia) 

 on a branch of the 

 cherry 



, , . . . , . The branches become 



and distorted ovaries, or grains whose tis- dist or te d, and long 

 sues have become filled and destroyed by cracks are formed, 



.1 ,. P ,, P /^VT . m-i greatly impairing 



the mycelium of the fungus (Claviceps). The the str ength of the 

 ergot represents a sort of resting stage in trees 

 the life history of the fungus, and from it are developed in the 

 spring purplish stalks bearing the sac fruits (Fig. 224, B). 



