8 THE CHEMISTEY OF THE FAEM 



taken up by the roots are converted into ammonia, 

 the ammonia into amides, and the amides finally into 

 albuminoids. 



The fatty matter of a plant may be formed from 

 carbohydrates; or possibly from the splitting up of 

 albuminoids. 



The vegetable acids in a plant are probably formed 

 by oxidation ; most likely by the oxidation of some of 

 the carbohydrates. 



3. Bespiration. — We have just referred to oxidation 

 as taking place in the plant. This is always going on 

 in the interior during life, and as a result the plant is 

 continually consuming a small quantity of oxygen, and 

 giving out a small quantity of carbonic acid, an opera- 

 tion precisely similar to animal respiration. In the 

 case of a green plant, this action is not readily per- 

 ceived during the daytime, being hidden by the opposite 

 action of the chlorophyll cells, which absorb carbonic 

 acid and evolve oxygen. If a plant is placed in dark- 

 ness the respiratory action becomes manifest. The 

 oxidation of matters already formed is an important 

 means for the production of new bodies. 



Plants destitute of chlorophyll behave, as a rule, 

 like animals ; they consume much oxygen and give 

 out carbonic acid. 



4. Transpiration. — While some evaporation of water 

 will occur through the cuticle of young plants, the 

 transpiration of water vapour cliiefly takes place 

 through small openings, known as stomata, which are 

 generally most abundant on the underside of the 

 leaves. These stomata open widely when the plant is 

 well supplied with water, and close more or less com- 

 pletely during drought ; the rate of evaporation is thus 



