MILDEW, &C. 47 



which it is liable, and which differ from the kinds infesting 

 nearly similar vegetables. 



50. The universality of the appearance of the simpler kinds of 

 Fungi, such as mould, mildew, &c. upon all spots favourable 

 to their development, has given rise to the belief that they were 

 spontaneously produced by the decomposing substances. But 

 there is no occasion for this mode of accounting for it ; since the 

 extraordinary means adopted by Nature, for the production and 

 diffusion of their germs, suffices to explain it. The duration of 

 the lives of individuals among the Fungi is very brief; their tis- 

 sue is soft and succulent, sometimes containing so little solid 

 matter, as almost to melt away when broken down ; and never 

 possessing any considerable amount of firmness. Now in the 

 Algae, where we have seen the development of the individual 

 taking place to such an enormous extent, the fructification is 

 generally obscure, and sometimes even scarcely perceptible. But 

 in the Fungi, all the energies of the plant seem directed to the 

 production of the germs of new ones ; its own size seldom attains 

 any great extent ; but the number of these germs is often almost 

 incalculable. Thus, the fine dust which issues from the common 

 Puff-ball when mature, consists entirely of these little bodies, 

 which are diffused through the air, and seem to float about in it, 

 ready to develop themselves when they meet with the fitting 

 conditions. In a single Fungus, above ten millions have been 

 counted ; and these were probably by no means the whole num- 

 ber contained in it. When these minute germs are once spread 

 through the air, there are so many means provided for their dif- 

 fusion, that it is difficult to conceive of a place from which they 

 should be excluded. 



51. However improbable, then, it may at first sight appear, 

 that every portion of the air we breathe should contain the germs 

 of a large number of species of Fungi, ready to develop them- 

 selves whenever the peculiar conditions adapted to each kind are 

 presented, there seems good reason to believe, that such is the 

 case ; and in this manner we may account for several facts, of 

 some practical importance, relative to the production of those very 

 troublesome forma of vegetation, known by the names of mould, 

 mildew, &c. It is well known that fruit-preserves are very 



