388 Illinois State Laboratory of Natural History. 



penetrate the epidermal cells, serving for the secure attachment 

 of the fungus, and probably also for its nourishment. These 

 haustoria present several forms, and they are of some impor- 

 tance in the classification of the species. In some cases the 

 haustorium simply consists of a slender tube v^hich penetrates 

 the epidermal cell of the host, within which it swells to an 

 oval or club-shaped sac, filled with granular protoplasm. More 

 often there is an external appendage or sucker, that is pressed 

 close to the surface of the epidermal cell; and from this, or 

 from near it on the mycelial thread, the haustorium proper 

 takes its rise and penetrates the epidermis. This external ap- 

 pendage may be smooth and entire, merely constituting a hem- 

 ispherical swelling on the mycelial thread; or, it may take the 

 form of a flattened disk with an indented margin. In the 

 latter case they are said to be "lobed," in the former, "not 

 lobed." 



The conidia, or asexual reproductive bodies, are cylindrical, 

 oval or nearly orbicular, simple, colorless cells filled with pro- 

 toplasm. They are formed by constriction at the ends of short, 

 simple, erect, rather stout, septate, colorless branches of the 

 mycelium, called fertile hyphae or conidiophores. A septum 

 forms near the end of the young hypha, and the walls at this 

 point become constricted. The cell thus cut off usually 

 swells a little, and at length falls away as a mature conidium. 

 Before this happens, however, other constrictions have taken 

 place below, thus forming a chain of nearly mature conidia 

 adhering end to end. Under favorable conditions they germi- 

 nate quickly, sending out a slender tube, which, on the proper 

 host, soon develops into a new mycelium. They are produced 

 in immense numbers throughout the growing season, and, as 

 they are very light and easily carried by the wind, they serve 

 for the rapid increase and wide distribution of the parasite. 



Other reproductive bodies arise, like the fruits of higher 

 plants, from a process of fertilization. The process has been 

 carefully studied by De Bary and others. It differs slightly in 

 the different genera. In those with a single ascus (Sphcero- 

 theca and Podosphcera) it is as follows: — 



Where two threads of the mycelium approach or cross 

 each other, a short special branch arises from each. One of 



