FUNGI IMPERFECTI 



303 



The germ tubes arise from any cell of the spore, and it is 

 stated that they may enter the host either by means of the 

 stomates or by directly penetrating the cuticle. This fungus 

 grows vigorously in pure cultures. Upon prune agar it has 

 been found (Jones) that the spores might be produced as a 

 chain of two, and on account of this character the plant has 

 been placed in the related genus Alternaria. As is, of course, 

 well known, the step 

 from Macrosporium 

 to Alternaria is at 

 best a very slight 

 one, yet it should 

 be remembered that 

 these genera based 

 upon recognizedly 

 variable characters 

 serve at most for 

 convenience. The 

 catenulate method 

 of spore production 

 has been reported 

 only in artificial cul- 

 tures in this case, 

 and it is possible, 

 furthermore, to ob- 

 tain for various 

 fungi in such cul- 

 tures in general 

 many variations 

 from what would be considered the normal type of spore production 

 upon the host. Attention may be called to the fact that cultures 

 of 'many Stilbeae yield upon agar only simple conidiophores. Cul- 

 tures of Fusarium and Glceosporium are also modified in an equiva- 

 lent manner, the stromatic development being usually suppressed. 

 Species of Cercospora also produce spores in an abnormal manner. 

 Upon the leaf Macrosporium may be accompanied by one or more 

 species of true Alternaria, but the latter are saprophytic, as deter- 

 mined by experimental work. 



FIG. 137. MACROSPORIUM SOLANI : GERMINATING 



SPORES WITH HYPH^E ENTERING STOMATA 



(After Jones) 



