FIG. 20. Phytophthora infestans, a fungus whose asexual reproductive 

 bodies are usually motile zoospores. The sexual mode of reproduction 

 has disappeared. In allied species the conidia do not contain zoospores, 

 but produce a germ-tube on germination. This sometimes happens with 

 P. infestans, which thus illustrates a fungus occupying a transitional stage 

 between the older aquatic types which constantly produce zoospores, and 

 the more modern types, where the conidia are dispersed by wind, and on 

 germination produce a germ -tube or hypha, which enters the host, i, a 

 cluster of branched conidiophores emerging into the air through the stoma 

 of a potato leaf; 2, a free conidium showing its contents breaking up into 

 zoospores ; 3, a conidium liberating its zoospores ; 4, a zoospore that has 

 become passive and is germinating by emitting a germ-tube ; 5, a conidium 

 germinating by the protrusion of a germ-tube. All figs. mag. 



