25G STRUCTURAL BOTANY 



fructification therefore serves for rapid propagation during 

 the summer, though, as we shall see, it is not of necessity 

 limited to that season. 



Later in the year another kind of spore, borne on the 

 same mycelium with the uredospores, begins to make 

 its appearance. The external sign of the change of 

 fructification is a change in the colour of the sori, from 

 orange-red to dark brown or nearly black. This is due 

 to the development of the teleutospores, which owe their 

 name (meaning final spores) to the fact that they appear 

 at the end of the season of growth. 



It was to the teleutospore form of fructification that 

 the name Puccinia was applied in the first instance, 

 before the life-history was completely understood ; for 

 this Fungus was originally put in three distinct genera, 

 which are now known to represent stages in the develop- 

 ment of one and the same plant. The teleutospore 

 condition is popularly known as the Mildew of wheat and 

 other cereals. The teleutospores are produced in just 

 the same way as the uredospores ; in fact both kinds of 

 spore are often found in the same sorus (Fig. 105, E), 

 during the intermediate period while the one fructifica- 

 tion is being gradually replaced by the other. Later in 

 the season we find sori consisting of teleutospores only 

 (Fig. 10 5, A). 



The teleutospore is borne on a stalk like the uredo- 

 epore, but is quite different from it in structure. The 

 membrane is excessively thick, consisting of a stout outer 

 coat of a dark-brown colour, and an inner colourless 

 layer. The spore is made up of two cells, separated by 

 a comparatively thin transverse septum. We may, if we 

 like, regard the whole structure as a sporangium containing 

 two spores ; but as they never become separated, it is 



