40 DISEASES OF TROPICAL PLANTS 



CH. 



The mycelium ramifies through, the tissues of the 

 leaves and eventually produces the conidiophores which 

 grow outward through the stomata. The character of 

 these conidiophores and conidia vary somewhat in the 

 different species, but the conidia in most cases produce 



FIG. 24. Peronospora Schleideni, a fungus with a much-branched conidiophore. 



1, A conidiophore that has emerged into the air through a stoma in an onion leaf 

 2, free conidia ; 3, oospore or resting-spore. All magnified (after Massee). 



zoospores. These zoospores germinate readily and the 

 disease spreads rapidly. In many species the oospores 

 are rather uncommon, and in some species entirely un- 

 known. 



Sclerospora is a genus with but few species, the 

 most important of which is S. graminicola (Sacc.) 

 Schroet. (see page 97), which attacks the grasses. 



