PERONOSPORALES 



201 



relative diagnostic value. Buisman summarizes the situation 

 with the statement that although theoretically no sharp line can 



Fig. 72.- — Phytophthora spp. (a-e) Germination of sporangium by swarmspores, 

 the spores passing first into a vesicle. (/) Sporangiospores which failed to 

 escape germinating by germ tubes in the sporangium, (g) Secondary sporangia 

 developed at tip of germ tube of primary sporangium, (h) Sporangiophores of 

 Ph. phaseoli arising from a stomate of lima bean, (m) Sporangiophore of Ph. 

 infeatans. (n) Oospore germinating by a germ tube on which sporangia then 

 form, (.s) Oogonium, basal antheridium, and oospore in Ph. erythro.^cptica. 

 (t) Oogonium, lateral antheridium, and oospore in Ph. cactorum. (u) Germina- 

 tion of oospore by simple germ tube. (/(, after Thaxter 1889; m, after Schwarzc 

 1917; others after Rosenbaum 1917.) 



be drawn between the two genera it is usually possible in practice 

 to determine whether a given form belongs to the Phytophthora 

 type or to the Pythium type. 



