CHAPTER IX. THE THALLOPHYTA. 323 



darker, almost blackish color. This is due to the development 

 of another kind of spores called teleutospores. These differ from 

 the others in being two-celled and having thicker walls. More- 

 over, they are not capable of developing on a healthy blade of 

 grass, but rest over winter in the straw, and in the spring germi- 

 nate, producing a promycelium the branches of which bear spo- 

 ridia. These are wafted away by the winds and germinate on 

 the leaves of the Barberry and, perhaps, on other plants, but not 

 on the Wheat. These immediately produce hyphae which, pene- 

 trating the stomata, form a mycelium which derives nourish- 

 ment from the cells of the leaf, and finally bursts through the 

 epidermis and forms the aecidium fruits popularly known as 

 "cluster-cups." 



In these little cups are formed multitudes of small, rounded, 

 yellow or orange-colored spores which the wind scatters. These 

 do not germinate on the Barberry, but those which are conveyed 

 to the leaves of grasses develop hyphae, which penetrate to the 

 interior of the leaf, and after a time produce the rust-like patches 

 at the surface. 



Some of the steps in the reproduction of this plant are shown 

 in Figs. 524, A, B and C. 



The phenomenon of alternation of generations, so prominent 

 in this group, also occurs in some others and is likewise exem- 

 plified in some of the lower forms of animal life. 



Other familiar plants belonging to the ^cidiomycetes are 

 Uromyces Beta?, the rust of Beet-root ; U. Pisi, a rust which 

 preys upon many Papilionaceous plants ; Chrysomyxa Abietis, 

 a species parasitic on the leaves of Spruces and which produces 

 golden-yellow teleutospores, and Puccinia straminis, which forms 

 its aecidium-fruits on the leaves of the Borrages. 



The Basidiomycetes. 



The distinctive characteristic of this group is the fact that 

 at the ends of the spore-bearing hyphae, large, club-shaped or 

 oblong cells are produced which bear at their apex delicate pro- 

 cesses called sterigmata, two, eight or, more commonly, four in 

 number, each of which is terminated by a rounded or ellipsoidal 

 spore. The cells which bear the sterigmata are called basidia, 

 and the spores, basidiospores. The basidia occur in large num- 



