INTKODUCTION TO CRTPTOGAMIC BOTANY. 261 



assume on their first development a form very different from 

 that of the full-grown plants. Before the common species of 

 Penicillium and Aspergillus, little gelatinous specks of 

 various colours frequently appear, which consist of a mul- 

 titude of granules, too small to admit of accurate measure- 

 ment, which, in all probability, are a condition of those 

 species. 



259. Fungi are unfortunately injurious to man, not only 

 from their deleterious qualities, but from the direct influence 

 which they exert on many members of the vegetable world, 

 and especially on those which furnish a great portion of his 

 food. Every kind of corn has its own peculiar parasites, which 

 either prey upon the grain directly or impair its quality, and 

 there are some species which are to a great degree common 

 to all. Corn, however, is not the only agricultural produce 

 which suffers ; potato crops have for years been ravaged by 

 Botrytis infestans, which destroys the leaves and haulm, and 

 finally infests the tuber, at last reducing it to a mass of putres- 

 cence. The Oidium, or rather the Erysiphe, of the vine, has 

 ruined the vine-growers in almost every country where it is an 

 object of cultivation. The year 1854, from the same cause, 

 proved in many districts most disastrous to the hop-growers, 

 except where precautions had been taken to dress the crops 

 with sulphur, which, when applied sufficiently early, appears 

 a specific for that and allied species of mildew. Many other 

 minor instances of loss might be enumerated, due to the same 

 cause. It has also been conjectured, that decay in fruit arises 

 from the attack of Fungi, but this appears to be a mistake, 

 except as a secondary cause. There is no doubt that decay is 

 much accelerated by the presence of Fungi, but not till some 

 previous lesion has existed. If, for instance, a portion of 

 the tissue of a fruit be exposed to the air, the vitality of the 

 divided cells is impaired, the albuminous matter set free acts 

 as a ferment, in consequence of which neighbouring cells are 

 involved, Fungi are established on the decomposing matter, 

 the mycelium of which penetrates into the succulent mass, at 

 whose expense it feeds; those threads which have gone through 

 their course decay, and in their turn act on the cell-walls 



