PROTOBASIDIOMYCETES 385 



on the other. The production of spores, particularly the produc- 

 tion of uredospores, is frequently in the nature of rust-like masses 

 from which has been derived the common name applied to this 

 family. Popularly the term rust has also been applied to certain 

 leaf spot fungi, but this usage is ill advised. 



This order appears to be somewhat closely related to the smuts ; 

 the presence of a promycelium (promycelial-like structure in the 

 latter) giving, of course, the chief clue to this relationship. On 

 the other hand, however, neglecting the feature of parasitism, 

 there is a close relationship with the saprophytic Auriculariales, 

 especially if we regard the teleutospore (promycelium, etc.) of the 

 rusts as the all-essential spore form. 



The mycelium is generally local. In special cases, however, it 

 may penetrate through a considerable extent of the host, and it is 

 also occasionally perennial. It is almost invariably intercellular, 

 abundantly branched, rather closely septate, and provided with 

 haustoria. The effect of the mycelium upon the host is not to kill 

 directly. In fact, the mycelium may develop within a tissue to an 

 enormous extent, yet the cells of the invaded tissue may remain 

 completely functional ; and death may result only when, after 

 abundant fruiting of the fungus, the rupture of the epidermis is 

 considerable, and doubtless the withdrawal of nutrients excessive. 

 The spores which may be produced are of five general types, as 

 given below. 



Spore forms. (1) Spermatia (or pycnospores), in spermogonia 

 (or pycnidia) ; (2) aecidiospores, in cup-like organs, secidia ; (3) 

 uredospores, in pustules or sori ; (4) teleutospores, in sori simi- 

 lar to the last ; (5) sporidia, upon a promycelium developed 

 directly from the teleutospore. 



A species may include from one to five (all) of these types. 

 The relations of these types one to another is definite and the 

 number is ordinarily constant in the species. 



The spermatia are minute spores produced in flask-shaped 

 conceptacles (spermogonia or pycnidia). They are supposed to be 

 now generally functionless. Many mycologists assume that they 

 had originally the function of one sexual gamete. The spermo- 

 gonia are commonly associated more or less closely with the 

 cecidia, although they may be associated with other spore types. 



