ELEMENTS OF ORGANIC STEUCTUEE. 223 



Cellular Plants. — In those classes of vegetation which 

 depart structurally to the least degree from the seed, and 

 which belong to what are called the " lower orders,"* we 

 find plants which consist entirely of cells throughout 

 all the stages of their life, and indeed many are known 

 which are but a single cell. The phenomenon of red snow, 

 frequently observed in Alpine and Arctic regions, is due to 

 a microscopic one-celled plant which propagates with great 

 rapidity, and gives its color to the 

 .(Q 1/ surface of the snow. In the chem- 

 ist's laboratory it is often observed 

 that, in the clearest solutions of 

 salts, like the sulphates of soda and 

 Fig. 37. magnesia, a flocculent mould, some- 



times red, sometimes green, most often white, is formed, 

 which, under the microscope, is seen to be a vegetation 

 consisting of single cells. Brewer's yeast, fig. 27, is nothing 

 more than a mass of one or few-celled plants. 



In the mushrooms and sea-weeds, as well as in the moulds 

 that grow on damp walls, or upon bread, cheese, etc., and 

 in the brand or blight which infests many of the farmer's 

 crops, we have examples of plants formed exclusively of 

 cells. 



All the plants of higher orders we find likewise to con- 

 sist chiefly of globular or angular cells. 

 All the growing parts especially, as the 

 tips of the roots, the leaves, flowers, and 

 fruit, are, for the most part, aggregations 

 of such minute vesicles. 



If we examine the pulp of fruits, as that f'v 

 of a ripe apple or tomato, we are able, by 

 means of a low magnifier, to distinguish 

 the cells of which it almost entirely con- °' ""'• 



sists. Fig. 28 represents a bit of the flesh of a ripe pippin, 



* Viz. : the Cn/ptogams. including Moulds, and Mushrooms, (Fungi,) Mosses, 

 Fems, and Sea-Weeds, (Algce). 



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