THE FUNGI 261 



Uredo and Puccinia, was long described by botanists as 

 belonging to a distinct genus. 



When an dEcidium - fruit is to be produced, a 

 group of hyphse become densely felted together in an 

 intercellular space of the leaf ; the inner hyphae of the 

 group enlarge their cells, so as to give rise to a little 

 nest of apparently parenchymatous tissue, surrounded by 

 a web of ordinary mycelium ; at the base of this mass a 

 row of vertically elongated cells the liymenium (Fig. 

 106, B, h) is formed, and it is from these cells that the 

 spores are formed. Each cell of the hymenium divides 

 by transverse walls, and produces in basipetal order a 

 long string of spores, often separated from each other by 

 intermediate sterile cells (Fig. 106, C). In this way the 

 whole interior of the young ^Ecidium becomes filled up 

 by numerous parallel chains of spores, which, as they 

 grow, completely displace the cellular tissue by which 

 the space was at first occupied. The wall or peridium 

 of the cup is built up of vertical rows of sterile cells 

 resembling the chains of spores, but connected together 

 into a permanent tissue. This peridium at first com- 

 pletely encloses the fruit, but as the spores within 

 increase in number, the enveloping layer is burst and 

 thrown open, showing a toothed margin where its edges 

 were torn apart (Fig. 106). 



The secidiospores, which are of a bright yellow 

 colour, become separated by the breaking down of 

 the sterile cells between them. The spores have 

 a polygonal form, owing to mutual pressure while 

 enclosed in the peridium. Their walls are thick, and 

 each spore possesses six germ-pores or pits, through 

 which, on germinating, the hyphse make their exit. 



The secidiospores germinate very readily, within a 



