244 HOW CROPS GROW. 



Cellular Plants. In the simpler forms or lower 

 orders * of vegetation, we find plants which, throughout 

 all the stages of their life, consist entirely of similar 

 cells, 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 surface of the snow. In the 

 chemist's laboratory it is often observed that in the clear- 

 est solutions of salts, like the sulphates of sodium and 

 magnesium, a flocculent mold, sometimes red, some- 

 times green, most often white, is formed, which, under 

 the microscope, is seen to be a vegetation consisting of 

 single cells. Brewers' yeast, Fig. 27, is nothing more 

 than a mass of one or few-celled plants. 



In sea-weeds, mushrooms, the molds that grow on 

 damp walls, or upon bread, cheese, etc., and in the 

 blights which infest 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 

 consist 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, aggrega- 

 tions of such minute vesicles. 



If we examine the pulp of fruits, as that of a ripe 



*Viz. : the Cryptogams, including Molds and Mushrooms (Fungi\ 

 Mosses, Ferns, Sea- Weeds (Algae) and Bacteria (Schizomycetes). 



