270 FIRESIDE SCIENCE. 



largest portion of their bulk, and therefore must 

 be regarded as of essential importance as food. 

 Before considering the sources and value of these 

 agents to vegetable structures, it will be interest- 

 ing to examine briefly the conditions under which 

 plants start into existence, and the forces or agents 

 which are involved in developing and sustaining 

 the embryo before the plant has the power of seek- 

 ing its own food. 



In all the changes and evolutions constantly 

 going- forward in the vegetable world, the sunbeam 

 plays a most important part. Analysis of a sun- 

 beam shows that it possesses three distinct functions 

 or powers. It is capable of supplying light and- 

 heat, and also it has actinic force, or the capability 

 of producing chemical decomposition and recompo- 

 sition. Upon the chemical -influence of the sun's 

 rays depends the germination of seeds, as well as 

 the growth of the plant. We bury the seed in the 

 ground and shut it out from the influence of light, 

 but we do not place it beyond the reach of the 

 sun's actinic influence, for that penetrates like heat 

 to the little earthy couch where the embryo plant 

 lies hid, and arouses it into life. Light, or the 

 luminous rays of the sun, so important to the well 

 being of the plant, is actually inimical to the excita- 

 tion of vitality in the seed. How singular is this 

 fact ! A series of carefully conducted experiments 



