222 BOTANY AND PHARMACOGNOSY. 



all the energy formed is used by the plantlet, much of it escaping 

 as heat, as in the germination of barley in the preparation of malt 

 (p. 575). Those plants dependent upon the presence of free 

 atmospheric oxygen are called aerobeSj while those which are 

 not thus dependent, as certain fungi and bacteria, are called 



xVN AEROBES. 



Metabolism. — Processes of construction and destruction are 

 going on simultaneously in the plant, and these are all grouped 

 under the general name of metabolism. The processes whereby 

 complex substances are built up from simpler ones, as in photo- 

 synthesis, are together spoken of as constructive metabolism 

 (anabolism), while those which involve the breaking down of 

 complex compounds into simpler ones, either through oxidation 

 or other chemical action, as when sugar is changed into carbon 

 dioxide and water, are grouped under the head of destructive 

 METABOLISM ( cataboHsm ) . 



