SOURCES OF TERRESTRIAL ENERGY 



and the short temperate winters, and the seed 

 will refuse to grow. Though nutritive material 

 may be at hand in abundance, there is no molec- 

 ular motion which the seed can absorb. When 

 the seed grows and shoots up its delicate green 

 stalk, tipped with a pair of leaflets, these leaflets 

 begin to absorb and transform those more rapid 

 waves of the sunbeam, known as light and ac- 

 tinism. That the plant may continue to grow, 

 by assimilating carbon and hydrogen, it is ne- 

 cessary for the leaf- molecules to decompose 

 the carbonic acid of the atmosphere, 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 indirectly by 

 the sunbeam. The slower undulations, pene- 

 trating 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 compound 

 molecules of the water. The swifter undulations 

 are arrested by the leaves, where they commu- 

 nicate their motor energy to the atoms of chlo- 

 rophyll, and thus enable them to dislodge adja- 

 cent atoms of carbon from the carbonic acid 

 in which they are suspended. And these chemi- 

 cal motions, going on at the upper and lower 

 extremities of the plant, disturb the equilibrium 

 3 2 9 



