Phytophthora infestans as it occurs in most parts of North America either is not biologically specialized or else the varieties of potatoes and tomatoes now grown are not kinds that reveal the presence of more than one form. The form prevalent in North America is the same as the one which occurred at Moscow in 1928 and at Munich in 1930. The demonstration of a biotype in Pomerania in 1932 may be attributed to a new form arising from the production of viable oospores of the fungus or to the fact that a hybrid possessingdemissum “blood” serves to bring out the existence of such a type.