284 



FUNGOUS DISEASES OF PLANTS 



The fungus. The mycelium penetrates the bark and later the 

 wood beneath to a considerable extent. The course of the fungus 

 through the bark and wood is very largely through the paren- 

 chymatous and medullary cells. From these, however, it infests 

 neighboring tissues, especially the xylem vessels. The stromata 

 and fruit bodies are developed from the latter part of the summer 

 into the autumn and winter. From the upper surface of the 

 stroma a mat of conidial hyphae arises. These break through the 



epidermis and underlying fun- 

 gous tissue. The conidia are 

 simple, hyaline spores which 

 apparently do not readily ger- 

 minate. Later in the season 

 the underlying stromatic tis- 

 sue which is now cup-shaped 

 shows the development of 

 flask-shaped perithecia sunken 

 in that portion of the stroma 

 which is made up chiefly of 

 fungous tissue. Bordering the 

 stroma a black line of more 

 abundant fungous tissue is 

 also evident. The body of the 

 perithecium is elliptical or 

 ovate at maturity, and it is com- 

 pletely filled with long-cylin- 

 drical asci about 160 x 13/4. 

 The asci are thick-walled with 

 terminal pore, and contain at maturity eight more or less spher- 

 ical, brown spores. The latter often measure 13 x IO/A, and a clear 

 space along one side indicates the line of rupture during germina- 

 tion. Twin germ tubes are invariably developed. 



Control. Observations on the progress of this disease would 

 seem to indicate that this fungus gains entrance through wounds, 

 and prevention consists in avoiding as far as possible the im- 

 proper injuries due to careless methods of pruning, cultivation, 

 and harvesting. Moreover, the cankered areas on limbs should 

 be pruned out and destroyed when found. 



FlG. 126. NUMMULARIA DISCRETA : THE 

 BLISTER CANKER FUNGUS 



a, stroma ; b, perithecium ; c, ascus 



