PROTOPHYTIC AND OTHEK FUNGI. 323 



319. The ' entophytic ' Fungi which infest some of the Vegetables 

 most important to Man as furnishing his staple articles of food, constitute 

 a group of special interest to the Microscopist; of which a few of the chief 

 examples may be here noticed. The mildew which is often found attack- 

 ing the straw of Wheat, shows itself externally in the form of circular 

 clusters of pear-shaped asci or spore-cases (Fig. 205), each containing 

 two compartments filled with sporules;' these (known _as the Puccinia 

 graminis) arise from a filamentous tissue constituting its mycelium, the 

 threads of which interweave themselves with the tissue of the straw; and 

 they generally make their way to the surface through 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 essenti- 

 ally distinct from that just described, consisting 

 of oval spore-cases, which grow without any regu- 

 larity 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. Hen- 

 slow, it seems certain that ' rust ' is only an earlier 

 form of * mildew;' the one form being capable 

 of development into the other, and the fructifica- 

 tion characteristic of the two supposed genera hav- 

 ing been evolved on one and the same individual. 

 It is another reputed, species of Uredo (the U. 

 segetum), which, when it attacks the flower of the 

 wheat, reducing the ears to black masses of sooty 

 powder, is known as smut or dust-brand. The 

 corn-grains are entirely replaced by aggregations of ^^ fe in{B or 

 spores; and these, being 01 extreme minuteness, Mildew, 



are very easily and very extensively diffused. The 



bunt or stinking rust is another species of Uredo (the U. fcetidd), which 

 is chiefly distinguished by its disgusting odor. 



320. The prevalence of these Blights to any considerable extent seems 

 generally traceable to some seasonal influences unfavorable to the 

 healthy development of the cereal; but they often make their appear- 

 ance in particular localities through careless cultivation, or want of due 

 precaution in the selection of seed. It maybe considered as certain that 

 an admixture of the spores of any of these Fungi with the corn grains 

 will endanger the plant raised from them; but it is equally certain 

 that the fungi have little tendency to develop themselves in plants 

 that are vegetating with perfect healthf ulness. The wide prevalence of 

 such blights in bad seasons is not difficult to account for, if it be true (as 

 the observations of Mr. John Marshall several years since rendered prob- 

 able) 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 unfavorable season should favor their development by 

 inducing an unhealthy condition of the wheat-plant. The same general 

 doctrine probably applies to the Peronospora, which has 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 



