on THE WHITE RUST OF CABBAGES. 269 



grow exclusively on languishing or decaying organisms. Pre- 

 judice to the contrary is so very strong and general, and is still 

 in ignorance of facts bearing on the subject, so often put for- 

 ward, that the real state of the case requires to be frequently 

 pointed out ; especially since incorrect preconceptions on this 

 subject may be of very evil consequence in minute research as to 

 the origin of disease both in the animal and vegetable kingdom. 



Almost every one is now agreed as to the real nature of Ure- 

 dinese since the observations of Leveille and Corda, which have 

 been confirmed by a host of microscopical observers. Only a 

 few German speculators, in their zeal for spontaneous or equi- 

 vocal generation, still adhere to the views of linger, that they 

 are mere transformations of the tissues from which they spring. 

 An incidental observation to this effect occurs in a late number 

 of the ' Botanische Zeitung.' 



The structure of the white rust of which we have been speak- 

 ing, differs so much from that of most other allied forms, that it 

 is strange that it should not have been ascertained before. 

 There is indeed in the work of Unger, on what he calls tlie 

 Exanthemata of plants, a correct figure as far as it goes, tab. 

 VI. f. 32, but he has merely given the cysts from which the 

 spores spring, each terminated by a single globose spore. This 

 is the more remarkable, because he was the first to describe the 

 spores of ^cidium as arranged in moniliform threads, a struc- 

 ture which has been beautifully illustrated by Coi'da, and which 

 any one can easily convince himself is correct. The moniliform 

 threads are not less visible in the white rust, and the spores are 

 connected with each other by a short cylindrical process exactly 

 as in some species of Oidium. The iDcst way to observe the 

 structure, as indeed is the case with all epiphytal fungi when 

 practicable, is to make a thin vertical section, which will exhibit 

 not only the necklaces of spores, but the obovate cysts from 

 which they spring, and the curious irregularly branched, often 

 thick and nodose greenish mycelium, which, as Mr. Broome 

 correctly observed to me, resembles more in form and general 

 habit the structure of HcBmatococcus Alman7ii than any other ve- 

 getable substance. Besides this irregular thick mycelium, there 

 are also fine mucedinous threads which penetrate deeper into 

 and amongst the tissues of the matrix, and resemble the more 

 usual form of mycelium in Uredinese. The figure of the general 

 structure of the species is by Mr. G. H. Hoffmann, that of the 

 younger state by Mr. Broome, and that of diseased panicles of a 

 sugar-loaf cabbage by Miss A. Vidal, who has made some 

 pleasing contributions to Miss Henslow's '■ Ocean Flowers.' 



Dr. Leveille has described the genus under the name of Cys- 

 lopus with very correct characters. It is to be wished, how- 



