CHAPTER XI. 



CHANGES OF ORGANIC MATTER IN THE PLANT. 



922. It has now been shown that under the influence of sun- 

 light green plants produce organic matter out of inorganic 

 materials. This organic matter is conveyed to points where it 

 is to be used, or to tcmporarj- reservoirs where it is stored for 

 future use. It undergoes manifold changes in the plant, until 

 in the ordinary course of nature it is resolved at last into the 

 verj- materials from which it originallj' came ; namely, carbonic 

 acid and water. 



923. Bnt as the organic matter of the plant represents in its 

 construction a definite amount of energy of motion derived from 

 solar radiance transformed into tlie enei'gy of position, in its 

 apparent destruction is involved the reconversion of this energy 

 of position into energy of motion. Between the first and last 

 terms of these constructive and destructive processes very differ- 

 ent periods of time may elapse in different cases, according to 

 the changes which the organic matter undergoes. 



924. That portion of the organic matter which is built into 

 the fabric of the plant in the form of cellulose more or less modi- 

 fled is not often broken down into its original components while 

 the organism is living; but, by decay and bj- combustion, even 

 this relatively permanent substance is decomposed, and its ele- 

 ments are finally given back to the air and soil. A certain por- 

 tion of the organic matter, however, undergoes speedy and 

 striking changes, and all of these are now to be examined 

 from another point of view. 



TRANSMUTATIOX, OR METASTASIS. 



925. The phj-siological expression for the substance formed 

 by chlorophyll in the sunlight is food. This substance is util- 

 ized by the organism in many waj-s ; but of these only the fol- 

 lowing need now be noticed: (I) for the supply of energy for 

 movements and other work ; (2) for the repair of waste ; (3) for 



