BLIGHTS OF CORN | POTATO-DISEASE ; VINE-DISEASE. 363 



the ' stomata ' or breathing-pores of its epidermis. The Rust, which 

 makes its appearance on the leaves and chaff-scales of "Wheat, has a 

 fructification that seems essentially distinct from that just described, 

 consisting of oval spore-cases, which grow without any regularity 

 of arrangement from the threads of the mycelium ; and hence it has 

 been considered to belong to a different genus and species, Uredo 

 rubigo. But from the observations of Prof. Henslow, it seems 

 certain that the Rust is only an earlier form of the Mildew ; the 

 one form being capable of development into the other, and the 

 fructification characteristic of the two supposed genera having 

 been evolved on one and the same individual. Another reputed 

 species of Uredo (the U. segetum) it is which, when it attacks 

 the flower of the Wheat, reducing the ears to black masses of sooty 

 powder, is known as Smut or Dud-brand. The Corn-grains are 

 entirely replaced by aggregations of spores ; and these, being of 

 extreme minuteness, are very easily and very extensively diffused. 

 The Bulit or Stinking Must is another species of Uredo (the 

 U. fostida), which is chiefly distinguished by its disgusting odour. 

 The prevalence of these Blights to any considerable extent 

 seems generally traceable to some seasonal influences unfavourable 

 to the healthy development of the "Wheat-plant ; but they often 

 make their appearance in particular localities through careless 

 cultivation, or want of due precaution in the selection of seed. 

 It may be considered as certain that an admixture of the spores of 

 any of these Fungi with the grains will endanger the plants raised 

 from them ; but it is equally certain that the fungi have little 

 tendency to develope themselves in plants that are vegetating with 

 perfect healthfulness. The wide prevalence of such blights in bad 

 seasons is not difficult to account for, if it be true (as the observa- 

 tions of Mr. John Marshall a few years since rendered probable) 

 that there are really very few Wheat-grains, near the points of 

 which one or two sporules of Fungi may not be found, entangled 

 among their minute hairs ; and it may be fairly surmised that 

 these germs remain dormant, unless an unfavourable season should 

 favour their development by inducing an unhealthy condition of 

 the wheat-plant. — The same general doctrine probably applies to 

 the Botrytis, which, from 1847 to the present time, has had a 

 large share in the production of the ' Potato-disease ;' and to the 

 Oidium, which has a like relation to the 'Vine-disease' that 

 was prevalent for some years through the south of Europe. 

 There seems no doubt that, in the fully-developed disease, the 

 Fungus is always present ; and that its growth and multiplication 

 have a large share in the increase and extension of the disorder, 

 just as the growth of the Yeast-plant excites and accelerates fer- 

 mentation, while its reproduction enables this action to be in- 

 definitely extended through its instrumentality. But just as the 

 Yeast-plant will not vegetate save in a fermentible fluid — that is, 

 in a solution which, in addition to Sugar, contains some decom- 



