GENERAL MORPHOLOGY OF PLANTS 



species. The fruit bodies (perithecia) are black or dark brown; 

 they occur singly, in troops or in masses, and sometimes are 

 imbedded in a black stroma (a compact sterile fungus tissue). 

 Many are saprophytes and many others are parasites on other 

 plants, causing leaf spots, blights, rots, cankers, knots, etc. 

 Many of these produce serious diseases of vegetables, farm crops, 



orchard and forest trees. Many 

 of them have conidial stages in 

 which asexual spores (called coni- 

 dia) are borne on stalks (free 

 hyphae called conidiophores), or in 

 other cases the asexual spores are 

 borne on short hyphae enclosed in 

 bottle-shaped or oval cases resem- 

 bling the sac fruit bodies. The 

 perfect stage is represented by the 

 true sac fruits, or fruit bodies, con- 

 taining the sacs or asci, the greater 

 number of the species having sacs 

 each containing eight spores. 



442. Examples of the black 

 fungi. A few only are briefly 

 mentioned here. The black knot of 

 plum and cherry (Plowrightia mor- 



bosa or Ottilia 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. 

 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. 



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

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



Fig. 239. 



Black knot of plum (Plowrightia 

 morbosa), showing deformities of the 

 stems. 



