ONION SMUT FUNGUS. 



127 



apparently there is no uniformity either in the position or number of 

 nuclei. The haustoria usually stain yellowish brown with the orange G 

 of the triple stain. 



Fig. 5. — Haustoria (A-E) and absorptive hyphal expansions (F, G). 



Absorptive Hyphal Expansions. 

 Frequently during the incubation period one finds the tips, especiallj' 

 of short lateral branches, flattened out like spatulas against the cells of 

 the host. In some sections, just before sporogenesis, these structures may 

 be found in great numbers. Usually they are terminal (Fig. 5, G), but 

 not infrequently they may be found intercalary within the ordinary 

 course of a hypha which, beyond the expansion, continues in its normal 

 size and shape (Fig. 5, F). They resemble the appressoria previously 

 mentioned as the bases from which the haustoria arise, but their number 

 is out of all proportion to the number of haustoria which one finds in the 

 same sections. No description of these organs has been given elsewhere, and 

 their function or meaning is not clear. One can only conjecture that their 

 purpose is to present a broad absorbing surface for securing more nourish- 

 ment from the host cells. It seems doubtful whether haustoria are really 

 necessary in this connection, because manj^ infections have been studied 

 under the microscope in wliich no haustoria could be found. 



