CHAPTER VIII 



PROTOBASIDIOMYCETES 



Uredinales 

 The rust-fungi, members of the group Uredineae, Uredinales or Aecidio- 

 mycetes, including over 1 700 species, are without exception obligate parasites 

 on the stems, on the sporophylls and especially on the leaves of vascular 

 plants, usually on those of angiosperms or gymnosperms but in one or two 

 cases of ferns. 



The mycelium ramifies in the tissues of the host, sends haustoria into 

 the cells, and may act as a local stimulant causing more or less marked 

 hypertrophy and consequent curling or malformation of the infected part. 

 Starch may be stored by the host, and this is so abundant in the hyper- 

 trophies caused by the aecidial mycelium of Puccinia Caricis on the nettle, 

 Urtica parvifolia, that they are eaten by the Himalayans; one or two other 

 species are similarly employed. Where the mycelium penetrates into the 

 perennial tissues of the host it is itself perennial. 



Spores and Sori. On the mycelium several kinds of spore are produced, 

 minute spermatia in spermogonia, aecidiospores in aecidia, uredospores and 

 teleutospores, sometimes mixed, sometimes separate, in more or less definite 

 sori. One or more of these types of spore may be lacking, but the teleuto- 

 spores are almost invariably present, and it is on them that the classification 

 of the group depends. 



Naturally enough it was some time before the various types of spore 

 were recognized as belonging to the same fungus and the old generic names 



Fig. 164. Germinating teleutospores ; a. Phragmidium bulbosum Schm. ; b. Triphragmidium Ulmariae 

 Lk.; c. Colcosporitim Sonchi Lev.; d. Uromy es appendiculatus (Fabae) Lev.; after Tulasne. 



