194 



The Plant World. 



the bark and into the wood. Later the stromata crack and rup- 

 ture the bark, exposinfi;^ the c^rav sy:ore-cushions, 1-8 to 1-4 inch 



Fig. 4. Nummularia discreta. (a) The black stromata have been left on the apple 

 branch after the bark has broken away. The stromatic rings on the wood show very di-;- 

 Cnctly. These characters are most prominent in a field diagnosis, (b) The bark has not 

 yet broken away. Tn some places the outer epidermis still covers the stromata. This gives 

 some idea of the relative abundance of stromata on the cankered portions. Some of the 

 rings on the wood show on the fractured end of the branch. 



in dia.r.eter. The stromatic tissue is hard and resistant and 

 rerr.ains in place after the bark has broken away. This is one of 



