98 



THE HARMONIES OF NATURE. 



include any mineral ingredient in its composition, is generally 

 divided by a sutural line into two equal halves, and often orna- 



Desmidiacese. 

 A, Staurastrum vestitum ; B, S. aculeatum ; c, S. paradoxum ; D, E, S. brachiatum. 



mented with spinous projections, presenting a very symmetrical 

 arrangement. These elegant little plants are fond of standing, 

 though not stagnant, water. Small shallow pools, that do not 

 dry up in summer, especially in open exposed situations, are 

 their most congenial homes. The larger and heavier species 

 commonly lie at the bottom, either spread out as a thin gela- 

 tinous substance, or collected into finger-like tufts. Other 

 species form a greenish or dirty cloud upon the stems and leaves 

 of other aquatic plants, where they serve as pasture-grounds for 

 Infusoria and other microscopic animals. 



The Diatomacece are likewise simple vegetable cells encased 



in a flinty envelope, consisting 

 of two valves, usually of the 

 most perfect symmetry, closely 

 applied to each other like the 

 valves of a mussel. The forms 

 of these minute organisms are 

 equally strange and beautiful, 

 exhibiting mathematical fi- 

 gures, circles, triangles, and 

 parallelograms, such as we find 

 in no other plants, while their 

 surface is often most elaborately sculptured and dotted with 



