i 5 8 TEXT-BOOK OF FUNGI 



number of species belonging to the Uredinaceae grow on 

 a different kind of host-plant during the different periods 

 of their complete cycle of development ; such are said to 

 be heteroecious, or metoecious as preferred by De Bary, 

 who first clearly described this phenomenon as presented 

 by Puccinia graminis. The teleutospores or resting-spores 

 of this fungus pass the winter on the dead culms of various 

 wild or cultivated kinds of grass. During the following 

 spring the teleutospores germinate in situ, producing 

 minute secondary spores that are dispersed by wind. 

 These secondary spores will not directly infect a grass 

 plant, but those that happen to be deposited on the surface 

 of a young barberry (Berberis vulgaris) leaf, germinate at 

 once, the germ-tube enters the tissues of the leaf and soon 

 gives origin to groups of aecidia or c cluster-cups ' crowded 

 with golden-yellow aecidiospores. Structures called sper- 

 mogonia also develop on the barberry leaf along with the 

 aecidia, and are supposed to represent male organs that 

 have persisted from a period when they were considered 

 to have been of functional value. 



The aecidiospores will not directly infect a barberry 

 plant, but when placed on the leaf of a suitable grass, 

 infection takes place, and in due course pustules of uredo- 

 spores appear on the surface of the grass leaf. Uredospores, 

 on the other hand, will only infect grasses, and the pro- 

 duction of uredospores and infection of new grasses con- 

 tinues throughout the summer. During the autumn, when 

 the host-plant is on the wane, the mycelium, that up to the 

 present had been producing uredospores, now commences 

 to produce teleutospores, in fact during the transition 

 period it is not unusual to find both uredospores and 

 teleutospores present in the same pustule. At a later 



