THE FUNGI WHICH CAUSE PLANT DISEASE 225 



elliptic, surrounded by a mucilaginous layer, 24-32 x 12-18 ju; 

 paraphyses exceeding the asci. 



The mycelium produces rot of cranberries, also leaf spots, but 

 the fructification of the fungus is rarely found in nature except on 



FiQ. 159. — ^A single perithecium 

 of A. vaccinii taken from a 

 pure culture on corn meal. 

 After Shear. 



Fig. 160. — Acan- 

 thorhynchus; a 

 germinating as- 

 cospore bearing 

 the peculiar 

 appressorium, 

 17, view from 

 above. After 

 Shear. 



old fallen leaves. In culture, however, it produces abundant peri- 

 thecia. When on the leaf the perithecia are subepidermal and 

 are sparsely scattered over the lower surface. No conidial or 

 pycnidial form is known. Remarkable appressoria are produced 

 by the germ tubes from the spores, Fig. 160. 



Sphseriacese (p. 222) 



Perithecia single or clustered, free or with a false stroma in 

 which they are more or less sunken; walls leathery, homy or woody; 

 ostiole rarely elongate, usually papillate; spores frequently ap- 

 pendaged. 



The family is distinguished by its free perithecia with papillate 

 ostioles. It contains about seven hundred species. 



Key to Genera of Sphsriacese 



Perithecia hairy above, rarely smooth above 

 and hairy beneath 

 Spores 1 or 2-celled 

 Perithecia thin, cuticulate or leathery 

 Spores 1-celled; asci apically thick- 

 ened 1. Niesslia. 



