The Anthracnose Disease of the Raspberry 165 



observed to be entirely subepidermal. The tissue of which it is composed 

 is in its mature condition hyaline, and varies from a pseud oparenchyma 



Fig. 16. ACERvuLus of plectodiscella veneta 



Section showing the differentiation in the upper and the lower layer of the stroma, also 

 the conidiophores arising in groups. Outlined with camera lucida from prepared slide. 

 The tissue is somewhat shrunken. X 850 



in the outer area to a plectenchyma next to the host cells. In the leaves 

 the stromatic tissue consists only of one to several layers of fungous 

 cells. The imperfect stage arises from this stroma both on the leaves 

 and on the canes, while the ascigerous stage has been observed to arise 

 only from the stroma on the canes. 



The ascocarps of P. veneta are pulvinate, from deep brown to black, 

 and about 75 /x in diameter (fig. 15). They are borne singly or in groups, 

 and they frequently anastomose and give rise to variously shaped bodies. 

 The dark color is due to a layer of thick- walled, brown cells which cover 

 each fruiting body. These cells at maturity split apart and expose the 

 tissue within, which is hyaline, pseudoparenchymatous, and usually in 

 a state of disintegration. The cells of the ascocarps are somewhat larger 

 and thinner- walled than those of the stroma. Globose, thick-walled asci, 

 from 24 to 30 ju in diameter, are scattered irregularly throughout the 

 interior of the fruit body and either lie against one another or are separated 

 by the fungous tissue. The ascospores are bonie parallel to one another 

 in the ascus. They measure from 18 to 21 /.: in length and from 6.5 

 to 8 )U in width, and are hyaline, four-celled, ovate, and slightly curved, 

 with constrictions at the septa. The basal cell is larger and more obtuse 

 than the apical cell. 



The imperfect stage of P. veneta has been known in literature as Gloeo- 

 sporium venetum Speg. Short, unb ranched conidiophores are produced, 

 frequently in groups over the surface of the stroma, and these bear unicellu- 

 lar conidia which are held together in a mucilaginous substance (fig. 16). 



275 



