MOULDS. 141 



them. The sucker-like bodies already described in 

 Gystopus are often found produced on the mycelium 

 of Peronosjiora, but occasionally they appear to be 

 absent, especially in the mould causing the potato 

 disease. 



From the mycelium erect threads are produced, 

 upon which one form of fruit, which may be 

 termed " acrospores," is borne. These filaments are 

 sometimes single, and sometimes in small tufts or 

 fascicles. In some instances they are considerably 

 branched, so as to present a dendroidal or tree-like 

 appearance; in others they are nearly simple, being 

 only surmounted by short spicules ; or, in one 

 instance, quite simple, and only surmounted by a 

 single acrospore. The branching habit is by far 

 the most common. 



Each ultimate branch in the ramification of the 

 fertile filaments engenders a single acrospore. Its 

 extremity, at first thin and pointed, swells in the 

 form of a globular vesicle, which soon takes the 

 elliptical or ovate shape of the perfected acrospore, 

 and at length separates itself from the branch that 

 supports it. 



In all instances the acrospores have a similar 

 structure, but with minute differences in form, &c, 

 * which have their importance in the determination 

 of species. In most cases the apex of the acrospore 

 is obtuse, and the entire body has a violet tint, 

 more or less deep ; in some it is completely colour- 

 less. These acrospores, when placed in favourable 



