CYSTOPUS, OR WHITE RUST. 143 



Rust. — Conidia unequal ; terminal cell sterile, larger than the 

 rest ; membrane thickened ; ochraceous ; fertile cells shortly 

 cylindrical ; membrane hyaline ; oospores globose ; epispore 

 brown, verrucose ; warts hollow, round, or irregular. This species 

 attacks Conipositce^ Goat's-Beard, Salsify, Scorzonera^ etc., and is 

 common in summer and autumn. De Bary states that he has 

 never found oospores on the Tragopogon^ although he found them 

 very plentifully on the Sco7'zonera. 



Cystopus candidus (PI. XVI., Figs. 19 — 21), Crucifer White 

 Rust. — Con'dia equal, globose; membrane equal, ochraceous; 

 oospores sub-globose ; epispore yellowish brown, with irregular, 

 obtuse warts ; warts solid. This species is the best known of all. 

 It is found on Shepherd's-purse, Cabbages, Horse-radish, and other 

 Criicife7-ce ; also on some few species of CapparidetE. It is 

 common in the summer. 



The following practical remarks by Worthington Smith will 

 well conclude this part of our subject: — "Alternation of crops 

 must tend to diminish white rust. Cabbages, cauliflowers, etc., 

 should not be grown for two years in succession where white rust 

 has prevailed. Weeds should be gathered together and burnt 

 when infected with white rust. No cabbage, cauliflower, turnip, 

 or mangel refuse should be allowed to remain in a decaying state 

 throughout the winter in the fields, for in these positions white 

 rust hibernates." * 



Having given a detailed account of this group of fungi, 

 we will now consider its position in the mycological world. The 

 classification of fungi is at present in an unsatisfactory state. It 

 is found that many supposed genera are only the early state or 

 condition of some other known fungi, and a constant process of 

 sifting and re-arranging is continually going on, especially amongst 

 the smaller and microscopic forms. Any clue to a scientific 

 classification deserves consideration, and of late years this has been 

 sought for, and apparently with some success, in the study of the 

 reproductive organs of fungi and the details of their life-history. 

 Classification on this principle may still be called artificial, but it 

 is natural, in so far as it attempts to bring into prominence actual 

 affinities, and not merely difterences and resemblances of external 

 * " Diseases of Field and Garden Crops." — \V. G. Smith. 



