FUNGI. 253 



account for all the phenomena. As an advocate of 

 the theory observes, " the fact that a certain number 

 of Uredines possess the faculty of passing a part of 

 their lives upon one plant, and the remainder of it 

 upon another, and a totally different one, is so re- 

 markable that until quite recently there were persons 

 who declined point-blank to believe it." Premising 

 that these sceptics still exist, we shall content our- 

 selves with a statement of the case, and its evidence, 

 without detailed arguments in opposition or defence. 



The first assumption of heteroecism is that, because 

 certain of the Uredines manifest themselves under 

 three forms, all should necessarily follow the same 

 type, especially those which occur on graminaceous 

 plants. To this it is objected that it has never been 

 proved that, in any case, the yEcidium form is essen- 

 tial to the production in nature of the Uredo and 

 Puccinia form. Further, that there are instances of 

 Uredo and Puccinia forms being commonly produced 

 on plants, other than the grass family, without the 

 intervention of any ^cidium forrri ; indeed, two en- 

 tire sections, called respectively Brachy-pticcinia and 

 Hemi-piiccinia, are of this character. Finally, it is 

 impossible, if such intervention were necessary, for 

 the limited supply of Alcidium berberidis in this 

 country to influence the enormous production of the 

 Uredo and Puccinia in corn, or its total absence in 

 Australia to effect the same result. 



The second assumption is that artificial cultiva- 

 tion, under artificial circumstances, affords proof that 

 the phenomena produced are identical with those 

 which would occur spontaneously in a state of nature. 



