en. vn.J SOURCES OF TERRESTRIAL ENERGY. 409 



tipped with a pair of leaflets, these leaflets begin to absorb 

 and transform those more rapid waves of the sunbeam, known 

 as light and actinism. That the plant may continue to grow, 

 by assimilating carbon and hydrogen, it is necessary for the 

 leaf- molecules to decompose the carbonic acid of the atmo- 

 sphere, and for the molecules of the rootlets to decompose the 

 water which trickles through the ground. But before this 

 can be done, the molecules of leaf and rootlet must acquire 

 motor energy, — and this is supplied either directly or in- 

 directly by the sunbeam. The slower undulations, penetrat- 

 ing the soil, set in motion the atoms of the rootlet, and 

 enable them to shake hydrogen-atoms out of equilibrium 

 with the oxygen-atoms which cluster about them in the com- 

 pound molecules of the water. The swifter undulations are 

 arrested by the leaves, where they communicate their motor 

 energy to the atoms of chlorophyll, and thus enable them to 

 dislodge adjacent atoms of carbon from the carbonic acid in 

 which they are suspended. And these chemical motions, 

 going on at the upper and lower extremities of the plant, 

 disturb the equilibrium of its liquid parts, and thus inaugu- 

 rate a series of rhythmical molar motions, exemplified in the 

 alternately ascending and descending currents of sap. And 

 lastly these molar motions, perpetually replenished from the 

 same external sources, are perpetually expended in the 

 molecular integration of vegetable cells and fibres. Thus all 

 the energy stored up in the plant, both that displayed in the 

 chemical activities of leaves and rootlets, and that which is 

 displayeu in circulation and growth, is made up of trans- 

 formed sunbeams. The stately trunk, the gnarled roots, 

 the spreading branches, the rustling leaves, the delicately- 

 tinted blossoms, and the tender fruit, are all — as Moleschott 

 no less truly than poetically calls them — the air-woven 

 children of light. 



In remote geologic ages untold millions of these solar 

 beams were occupied in separating vast quantities of carbon 



