136 THE MICROSCOPIST. 



ease among silkworms called "pebrine;" etc.; have a 

 strong analogy in their rapid multiplication to the yeast- 

 cells. * 



The sporules of any of the ordinary moulds, as Penicil- 

 lium, Mucor, or Aspergillus, will develop into yeast-cells 

 in a moderately warm solution of cane-sugar, showing 

 how differently the same type of bioplasm may develop 

 under different conditions. The term polymorphism has 

 been given to this phenomenon. Very many species, and 

 even genera, so called, may after all be only varieties of 

 the same kind of organism. 



In many morbid conditions of the skin and mucous 

 membranes, there is not only an alteration or morbid 

 growth of the part, but a vegetation of fungi. Thrown- 

 off scales of epithelium from the mouth and fauces exhibit 

 fibres of leptothrix, and the false membrane of diphtheria, 

 as well as the white patches of aphtha or thrush, show 

 the mycelia and spores of fungi. The disease in silkworms 

 called muscardiue is due to a fungus, the Botrytis bassiana 

 (Plate VIII, Fig. 104), whose spores enter and develop in 

 the air-tubes. The filamentous tufts seen about dead flies 

 on window-panes, etc., arise from a similar growth of 

 Achyla. In certain Chinese or Australian caterpillars, 

 this sort of growth becomes so dense as to give them the 

 appearance of dried twigs. Even shells and other hard 

 tissues may become penetrated by fungi. The dry rot in 

 timber is a form of fungus. 



The mildew which attacks the straw T of wheat, etc., 

 arises from the Puccinia graminis, whose spores find their 

 way through the stomata or breathing pores of the epi- 

 dermis. Rust, and smut, and bunt, originate in varieties 

 of Uredo. The "vine disease" and the "potato disease," 

 as they are called, have similar origin. 



Various methods have been proposed to destroy fungi 

 in growing plants, but it must be remembered that the 

 function of these organisms is chiefly to remove formed 



