INTRODUCTION TO CRYPTOGAMIC BOTANY. 323 



34?7. Besides the Ustilaginous species, tliei-e are others 

 which grow for the most part in definite tufts, and which con- 

 stitute the old genvis Uredo. Some of these are brown, but 

 the greater part are of a bright yellow, inclining often to 

 orange, while one genus, Cystopus, has spores of a pure white. 

 It is amongst these that the larger spores occur, which, though 

 often abundant, are scarcely ever so much so as to make them 

 disagreeable objects like the dusty Ustilagos. 



348. Most of the genera have merely the cuticle as a cover- 

 ing ; but in ^cidium there is a distinct peridium, consisting 

 of a single layer of closely packed cells, which, when the cuticle 

 of the plant bursts, protrudes, and either forms an irregular 

 sac, or bursts by means of radiating fissures, the laciniae curl- 

 ing back and presenting an elegant object for the microscope. 

 In some cases they are extremely numerous and linear, 

 in others they adhere above, allowing the spores to pass be- 

 tween them, as through the wires of a cage. In most cases 

 the matrix is only very slightly affected. The mycelium, 

 indeed, penetrates into and between the tissues, partially ex- 

 hausting them or oxydizing the chlorophyl, so that the leaves 

 on the parts opposed to the pustules exhibit autumnal tints. 

 Sometimes, however, the effect is most extraordinary. The 

 jEcidium of the Elder distorts and curls the stems till they 

 appear to be something totally different from the original 

 plant, while in other cases large gouty swellings appear, or the 

 inflorescence is entirely suppressed, and the peduncles alone 

 remain filled with reproductive matter. Those species of 

 Cissus which are infested with smut, have thus given rise to 

 a spurious Phaenogamous genus in Relllquice Haenkeanw. In 

 other instances, the change is considerable, though the original 

 outline is more perfectly preserved, as in those jEcidia 

 which attack the leaves of different species of Anemone. In 

 such instances the leaves, which will be eventually covered with 

 the Fungus, show that they are impregnated with its mycelium 

 as soon as they make their appearance. In some cases, as in 

 bunt, this is evident from the peculiar glaucous aspect assumed 

 by the infected stems. 



849. One genus, Ravenelia (Fig. 69, c, d), still requires to be 

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