146 BASIDIOMYCETES. 



lacese have gymnocarpic fruit-bodies, while those of the 

 Pilacraceae, on the contrary, are angiocarpic. 



Order 1. Uredinaceae (Rusts). All the Rust-Fungi are 

 parasites, their mycelium living in the interior of the stems and 

 leaves of their hosts, causing red, brown, or black spots hence 

 their name and malformations, sometimes of considerable size. 



The Rust-Fungi are gymnocarpic and destitute of a hymenium ; 

 for these reasons they are regarded as the simplest order of the 

 Basidiomycetes. They are entirely parasitic, and their filamentous, 

 branched mycelium ramifies in the intercellular spaces of its host, 

 and often protrudes haustoria into the cells. The mycelium is 

 perennial should it enter a woody tissue ; it may also hibernate in 

 the rhizomes of perennial herbs and permeate the shoots springing 

 from them, but in the majority of the Rust-Fungi the mycelium 

 has a very limited growth. The chief means of reproduction of 

 the Rust-Fungi are the chlamydospores, which in the more highly 

 developed species occur in three forms, namely, the teleuto-, 

 aecidio-, and uredo-spores. The spores, in the host, are formed 

 immediately beneath its epidermis, which is ruptured on the 

 ripening of the spores, with the production of "rust," brown, red, 

 or black spots. Those chlamydospores which produce basidia are 

 termed teleutospores. The spore on germination produces a trans- 

 versely divided basidium, " promycelium," on which basidio- 

 spores, " sporidia," generally four in number, are produced on 

 lateral sterigmata. This basidio-fructification is gymnocarpic; 

 the basidia neither form a hymenium nor a fruit-body (only 

 Cronartium and Gymnosporangium have a slight indication of a 

 basidio-fructification). 



Many Rust-Fungi, in addition to basidiospores, have small, 

 unicellular conidia, " spermatia," which are borne in conidio- 

 carps, " spermofjnnia" 



The TELEUTOSPORES (Winter-spores) maybe either unicellular or 

 multicellular ; in the majority of cases they are enclosed in a hard 

 outer cell- wall, the exospore, which in some cases is very strongly 

 developed ; they have also a long or short stalk, the remains of 

 the spore-bearing hypha. Each cell of the teleutospore has one 

 germ-pore (a thin portion of the wall, for the protrusion of the 

 germ-tube ; in Phragmidium and Gymnosporangium there are, how- 

 ever, several germ-pores). The colour of the teleutospores is 

 generally much darker than that of the uredospores, and it is by 

 these that the majority of the Rust-Fungi hibernate. 



