THE PA GE OF NA TUBE. 127 



lines or systems of life seem to start as it were from a 

 common point at the base ; the inferior forms bearing a 

 certain similarity to each other in structure and func- 

 tions, which gradually disappears as we ascend the scale 

 of development, until at the summit we behold those 

 vast differences which distinguish an elephant from a 

 palm-tree. 



In this class of plants, minute and obscure although 

 they are, the infinite resources of creative power are 

 perhaps more clearly and overwhelmingly revealed to 

 our perceptions, than in even the highest orders of the 

 vegetable kingdom. The most unwearied research, con- 

 tinued for centuries, has not yet assigned limits to that 

 amazing variety which is their most remarkable feature, 

 numbering as they do species that baffle classification, 

 and within which a still more astounding variety of in- 

 dividual types are to be found. 



Every one is familiar with that green slimy matter, 

 which during the spring and summer months creams 

 over the surface of the stagnant pool, the half dried-up 

 streamlet, or the wayside ditch ; but there are few who 

 regard it otherwise than as a disagreeable scum or im- 

 purity, to which in Scotland the expressive name of 

 slaak has been applied. It is in reality, however, an 

 aggregation of plants, perfect in all their parts, and 

 furnished with peculiar organs of nutrition and repro- 

 duction. Let us place a small portion of it on a concave 

 glass, containing a drop or two of water sufficient to float 

 it freely, and then place it under the microscope for ex- 

 amination, and what a beautiful spectacle is unfolded to 

 us ! That which to the naked eye. appears a mere 



