The Anthracnose Disease of the Raspberry 169 



mycelium is formed. When an ascus is placed in a drop of water or on 

 agar, the spores within germinate by sending the sterigmata through the 

 wall of the ascus and producing the sprout conidia on the outside. These 

 in turn germinate. After the production of the secondary spores the 

 ascospores shrivel and disintegrate. 



During the spring and early summer the ascospores are ejected from 

 the asci. Falling on the young shoots, apparently the spores produce the 

 sprout conidia which later send forth germ tubes that penetrate the host 

 tissue. Because of their gelatinous walls, the ascospores could readily 

 adhere to the smooth surface of the cane and germinate when sufficient 

 moisture is present. These steps, however, have never been followed by 

 the writer. 



The imperfect stage 



As stated above, Plectodiscella veneta may pass the winter in the asciger- 

 ous stage. The ascocarps, however, are very rare and the pathogene as 

 a rule winters over as mycelium in the canes. With the usual periods of 

 rainfall in the spring, accompanied by warm weather, a great many 

 conidia are produced in the old lesions, and these conidia readily infect 

 the young raspberry shoots which at this time are about eight to twelve 

 inches high. 



The germination of a conidium on a young raspberry cane has been 

 observed only on canes in a moist chamber. Here the spore germinates 

 by producing one or more germ tubes, which branch profusely and form 

 a minute cushion of cells. The cushion adheres closely to the host and 

 is not readily removed, evidently because of the hyphae which have begun 

 to penetrate the cell or cells of the host beneath. It is difficult to deter- 

 mine whether the minute fungous mass is subcuticular or not. On the 

 young shoots of the raspberry used (Riibus neglectus) the cuticle is poorly 

 developed. Later, however, when the fungus has spread through the 

 epidermal cells, the cuticle may be found to extend a short distance over 

 the lesion. After the pathogene has entered the cells of the host, further 

 growth continues in the formation of a stroma, the center of which appears 

 as a small pustule visible to the eye. This raised part of the stroma has 

 nothing whatever to do with the fructification of the fungus, as one is at 

 first led to believe, but is merely the accumulation of fungous cells at the 

 point of infection. While the tissue of the cane is tender the mycelium 

 grows rapidly, but growth is soon checked upon the hardening of the host 

 cells at maturity. Consequently a lesion resulting from a single infection 

 seldom reaches a width of more than one centimeter. With the further 

 tangential growth of the cane underneath the lesion, the stroma is often 

 torn apart, and during the second year it is found primarily about the 

 edges of the spot. 



279 



