6 PHYSIOGNOMY OF PLANTS. 



position in the laboratories of Nature, in the clouds and in 

 the pulsating vessels of animals and plants. Organic forms 

 also descend deep below the surface of the earth, wherever 

 rain or surface water can percolate either by natural cavities 

 or by mines or other excavations made by man : the sub- 

 terranean cryptogamic Flora was an object of my scientific 

 research in the early part of my life. Thermal springs of 

 very high temperature nourish small Hydropores, Conferva?, 

 and Oscillatoria. At Bear Lake, near the Arctic Circle, 

 Richardson saw the ground, which continues frozen through- 

 out the summer at a depth of twenty inches, covered with 

 flowering plants. 



We do not yet know where life is most abundant, 

 whether on continents or in the unfathomed depths of the 

 ocean. Through the excellent work of Ehrenberg, " Uber 

 das Yerhalten des kleinsteri Lebens," we have seen the sphere 

 of organic life extend, and its horizon widen before our eyes, 

 both in the tropical parts of the ocean and in the fixed or 

 floating masses of ice of the Antarctic seas. Siliceous- 

 shelled Polygastrica, and even Cosciuodiscse, with their green 

 ovaries, have been found alive enveloped in masses of 

 ice only twelve degrees from the Pole; the small black 

 Glacier flea (Desoria glacialis) and Podurellse inhabit the 

 narrow tubular holes examined by Agassiz in the Swiss 

 glaciers. Ehrenberg has shown that on several microscopic 

 Infusoria (Synedra, Cocconeis) others live as parasites, and 

 that in the Gallionellse such is their prodigious power of 

 development, or capability of division, that in the space of 

 four days an animalcule invisible to the naked eye can form 



