148 BASID10MYCETES. 



Chrysomyxa abietis). Other species have in addition uredospores; 

 others spermogonia and uredospores ; others spermogonia and 

 secidia ; others spermogonia, uredospores and secidia. Those 

 species in which all the methods of reproduction are not de- 

 veloped must not be considered as incomplete forms. 



As a rule the mycelium, which is produced from the basidio- 

 spores, developes secidia; in the species, however, without secidia, 

 it developes the uredo-form,~and when the uredospores are also ab- 

 sent, the teleutospore-form. It has been established in some species 

 of Puccinia and Uromyces that the formation of secidia can be sup- 

 pressed, and it is not a necessary part of the cycle of develop- 

 ment of the species. 



The majority of Bust-Fungi hibernate in the teleutospore-form. Many 

 species are able to hibernate in the uredospore-form (Coleosporium senecionis). 

 Others pass the winter in the aecidio-form, and develope aecidia on new hosts 

 (Uromyces pisi, on Euphorbia cyparissia* ; Phragmidium subcorticium, on Rosa; 

 Meidium elatinum, on Abies alba). In Chrysomyxa abietis, the mycelium,, 

 developed from the basidiospores, survives the winter. 



Among the Rust-Fungi, with several forms of reproduction,, 

 there are about sixty whose development can only be completed by 

 an alternation of hosts, that is, on one host only uredo- and teleuto- 

 spores are produced, while the further development of the ger- 

 minating basidiospores, and the formation of the secidia and 

 spermogonia from its mycelium, can only take place on a second 

 quite distinct and definite host (hetero&cious or metoxenous Fungi). 

 Those Fungi which have all their forms of reproduction on the 

 same host are termed autc&cious or autoxenous. It is not, however,, 

 always necessary that the hetercecious Rust-Fungi should regularly 

 change their hosts ; for example, Puccinia graminis can hibernate 

 in the uredo-form on the wild Grasses, and in the spring can dis- 

 tribute itself again in the same form. 



As a consequence of the alternation of hosts the various forms of develop- 

 ment were considered as independent genera (Uredo, sEcidium, Rastelia, Cccoma,. 

 Periderniium), until De Bary and Oersted established, about the same time 

 (1865), the mutual connection of some forms, and paved the way for the right 

 conception of these Fungi. 



As an example of one of the most highly developed species, 

 Puccinia graminis, the " Rust of Wheat," holds a prominent posi- 

 tion. Its uredospores and teleutospores are produced (Fig. 146) 

 on Grasses (on cereals, especially Wheat, Rye, Oats, and many 

 wild Grasses), while the secidia and spermogonia are confined to- 



