106 PRACTICAL BOTANY. 



mis, which normally covers over the tissues, is ruptured. 

 In case it is the leaf which has been cut, dark patches 

 may be observed as rupturing and projecting through 

 the epidermis of both the upper and lower surfaces. 



Put on a high power, and in a thin section 

 observe 



1. The thin hyphae of the branched mycelium of 

 the parasite (Puccinia), which ramify in the softer, 

 succulent tissues, but do not as a rule attack the 

 sclerenchyma, or vascular bundles : they may be traced 

 up to the dark patches above noted. 



2. The masses of dark brown teleutospores or 

 winter spores, which are produced by this mycelium, 

 each spore being borne on a thin pedicel : each consists 

 of two cells, with thick walls, differentiated into two 

 layers, the exospore and the endospore. In the 

 protoplasmic contents of each cell is a clear spherical 

 body, which may be the nucleus, but this is not certain. 



III. If pieces of a Grass plant bearing teleutospores 

 be kept in a moist atmosphere (on wet blotting-paper, 

 under a bell-glass) in the spring-time, a fine, white, 

 semi-transparent growth will be produced from the 

 teleutospores : this is the promycelium. Remove some 

 of these germinated teleutospores carefully with a 

 needle, and mount in water : if this be done without 

 injuring the promycelium, it will be seen under a 

 high power that one or both of the cells of the 

 teleutospore have put out a germinal tube (the pro- 

 mycelium) by rupture of the exospore, and protrusion 

 of the endospore : this promycelium divides into four 

 or five cells, each of which (excepting the basal one) 

 produces a conical process (the sterigma) : the end 



