i6o 



DISEASES OF TREES 



The aecidia appear on Sorbus Aria, S. Chamcemespilus, Pyrus 

 Mains, and Sorbus torminalis (?). 



The cushion-like stroma, on which the aecidia are often 

 arranged in circles, is very thick, and luxuriantly developed. 

 The pseudo-peridia are somewhat cup-shaped, and are split 

 up as far as the base into a large number of filaments I mm. 

 in length, which bend out somewhat. The aperture of the 



FIG. 89. G. tremelloides on 

 FIG. 88. ^Ecidia of J. communis. a a, teleu- 

 G. tremelloides on tospore-layers ; b b, scars 



a leaf of Sorbus which are left after the 



Aria. mucilaginous mass has 



dropped off. 



FIG. 90. Teleutospores of 

 G. tremelloides, a, basi- 

 dium ; b, spore that has 

 not yet germinated ; c, a 

 similar spore, showing 

 contraction along the 

 centre ; d, ditto with the 

 cells separated ; e, a 

 germinated teleutospore 

 with promycelium and 

 sporidium ; /*, basal view 

 of a teleutospore showing 

 three germ-pores, the 

 one from which the germ- 

 tube is issuing being 

 closed by a lamella. 



aecidium is distinct, and is black in colour owing to the dark 

 spores. Material sent by Herr Nawaschin, of Moscow, shows 

 that this species also occurs in Russia, where the teleuto form 

 develops not only in the cortex but also on the leaves of 

 Juniperus communis, forming an oblong cushion-like stroma 

 which extends over about half of the leaf. In that country the 

 aecidia occur on the leaves of the apple-tree. 



