PROTOPHYTIC AND OTHER FUNGI. 



321 



317. There are scarcely any Microscopic objects more beautiful than 

 some of those forms of ' mould' or ' mildew,' which are commonly found 

 growing upon the surface of jams and other preserves; especially when 

 they are viewed with a low magnifying power, by reflected light. For 

 they present themselves as a forest of stems and branches, of extremely 

 varied and elegant forms (Fig. 204), loaded with fruit of a singular deli- 

 cacy of conformation, all glistening brightly on a dark ground. In remov- 

 ing a portion of the ' mould ' from the surface whereon it grows, for the 

 purpose of microscopic examination, it is desirable to disturb it no more 

 than can be helped, in order that it may be seen as nearly as possible in 

 its natural condition; and it is therefore preferable to take up a portion 

 of the membrane-like substance whereon it usually rests, which is, in fact, 

 a mycelium composed of interlacing filaments of the vegetative part of the 

 plant, the stems and branches being its reproductive portion ( 321). 

 The universality of the appearance of these simple forms of Fungi upon 

 all spots favorable to their development, has given rise to the belief that 

 they are spontaneously produced by decaying substances: but there is no 



FIG,. 203 



-Fro. 305. 



Shell of Anomia penetrated by 

 Parasitic Fungus. 



Stysanus caput-medusce . 



occasion for this mode of accounting for it; since the extraordinary 

 means adopted by Nature for the production and diffusion of the germs 

 of these plants adequately suffice to explain the facts of the case. The 

 number of sporules which any one Fungus may develop is almost incal- 

 culable; a single individual of the puff-ball tribe has been computed to 

 send forth no fewer than ten millions. And their minuteness is such that 

 they are scattered through the air in the condition of the finest possible 

 dust; so that it is difficult to conceive of a place from which they should 

 be excluded. This universal diffusion was clearly proved several years 

 ago by an experiment made by Dr. Brittan, of Bristol; who caused air to 

 be pumped for several hours together through an inverted siphon, the 

 bend of which was immersed in a freezing mixture, so as to condense the 

 aqueous vapor of the atmosphere. The water at last came to be tinged of 

 a deep brown hue; and .was found, when microscopically examined, to be 

 charged with multitudes of sporules of Fungi. More recently, Prof. 

 Tyndall has shown, by a peculiar application of electric light, that all 

 ordinary air contains a multitude of excessively minute solid particles 

 suspended in it; that these, being for the most part destructible by heat, 

 are chiefly organic; and that they may be either strained off, so as to ren- 

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