MEMOIR XL] THE FORCE INCLUDED IN PLANTS. 177 



MEMOIR XI. 



OF THE FORCE INCLUDED IN PLANTS. 



Collected and condensed from Memoirs in the Journal of the Franklin Institute and 

 Harper's Monthly Magazine. 



CONTENTS : Growth of a seed in darkness and in light. Action of 

 plants and animals respectively on the atmosphere. Examination of 

 Rumford's experiments. Dark heat rays cannot decompose carbonic 

 acid. Germination in colored rays. Greening of leaves takes place in 

 the yellow and adjacent rays. The essential condition of all chemical 

 changes by radiation is absorption. Plants absorb force from the sun; 

 it is associated with their combustible parts, and is disengaged by oxi- 

 dation. 



I HAVE given in Memoir II. a description of the struct- 

 ure of an ordinary flame. Its light is derived from par- 

 ticles of solid carbon issuing from combustible matters 

 with which the wick or the gas jet is fed ; these solid 

 particles, passing from a low temperature to a white 

 heat, and undergoing eventually complete oxidation, es- 

 cape into the atmosphere as carbonic-acid gas. 



We now encounter a question of imposing interest: 

 Whence has the force which thus manifests itself as heat 

 and light been derived ? Force cannot be created ; it 

 cannot spring forth spontaneously out of nothing. 



It may be said, without much error, of such flame-giv- 

 ing compounds as we are here considering, that they are 

 for the most part compounds of carbon with hydrogen. 

 To regard them as such will very much simplify the 

 facts we have now to present. 



Under the form of oils and fats these combustible 

 substances are derived directly or indirectly from the 

 vegetable world ; directly, as, for instance, in the case of 



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