266 



GENERAL MORPHOLOGY OF PLANTS 



fruits, or fruit bodies, containing the sacs or asci, the greater 

 number of the species having sacs each containing eight spores. 



428. Examples of the black fungi. A few only are briefly 

 mentioned here. The black knot of plum and cherry (Plowrightia 

 morbosa or Otthia morbosa). This produces black rough excres- 

 cences on the limbs of living cherry and plum trees, which spread 

 from year to year, finally encircling the limbs and killing them. 



Fig. 229. 



Plowrightia morbosa, showing details of the fungus which causes the galls. A, section 

 through the velvety stroma. showing conidia bearing stroma. B, conidiophores and conidia 

 still more enlarged. C, a single perithecium containing asci and paraphyses. D, paraphyses 

 and asci containing spores still more enlarged. E, ascospores, one germinating. (After Farlow.) 



When a tree is badly infected it is an ugly sight. In early summer 

 the knots are covered with a black velvety growth of short erect 

 hyphae bearing the conidia. During the winter the sac fruits are 

 formed, and are thickly crowded over the surface of the knot, 

 the spores ripening along in February. These knots should be 

 cut out and burned, or badly infested trees removed and all dis- 

 eased branches burned. 



429. The cup fungi. These include a large number of sac 

 fungi which are mostly saprophytic, and grow on the ground, 

 rotten and dead wood, leaves, etc. Many of these belong to the 

 old genus Peziza. The asci are crowded over the upper surface 

 of the cup, and surrounded below and on the sides by the sterile 



