CH. IV, 8] RESPIRATION OF PLANTS 167 



of electricity, kinetic energy, is sent into the battery, and 

 there forcibly dissociates certain stable chemical compounds 

 into simpler substances; whilst these substances remain 

 apart the energy is latent, ready to come forth once more 

 in kinetic form (again an electrical current), when, by the 

 closing of a circuit, the substances are allowed to re-combine 

 into the old compounds. Food is nothing other than a stor- 

 age battery, charged in green leaves by the sun, and discharged 

 in the body by respiration. 



Thus it is plain why oxygen is necessary in respiration, 

 and therefore why both plants and animals have need of 

 "air." The parts of plants above ground have an ample 

 supply admitted through stomata and lenticels along the air 

 passages ; but the case is different with roots, for often the 

 air is expelled from the soil by the presence of water. This 

 is why wet soils must be drained, not to remove water, but 

 to introduce air. Where roots live continually in water, as 

 in bogs and swamps, the air supply is usually obtained 

 through large passages extending down through the stems 

 from the leaves; and it is the presence of these ample air 

 passages which gives the soft spongy texture to so many 

 marsh plants. 



That respiration is indispensable to all plant processes in- 

 volving growth and movement can be proven very strikingly 

 by methods which deprive the parts of oxygen, while leaving 

 them otherwise uninjured and ready for work. This is ac- 

 complished by use of an instrument called the anoxyscope 

 (" without-oxygen demonstrator") shown in our picture 

 (Fig. 116). 



The energy released in respiration is mostly applied to 

 various kinds of work involving motion, the circulation 

 of protoplasm, the enlargement of cell walls, and the like; 

 and on the completion and cessation of motion it is con- 

 verted into radiant heat. Thus all growing, and even all 

 living, parts are somewhat warmer than their surroundings. 

 A thermometer thrust into the opening flower of a Calla 



