THI. FOOD OF I'LANTS. 81 



process, and it is only when plants are in 

 darkness, either artificial or that ordinarily 

 occurring at night, that the fact that a plant 

 does really breathe out carbon dioxide like an 

 animal can be detected When later we try 

 experiments on the breathing of plants it is 

 essential to remember that the plants must 

 be kept in the dark. 



THE FOOD OF PLANTS. 



1. As the result of the building-up pro- 

 cesses which go on in the leaf we find that 

 starch is formed. In the practical work at the 

 end of this chapter experiments are described 

 which enable us to prove (1) that starch is 

 actually formed in leaves, .(2) that for this 

 formation of starch, by the living substance of 

 the plant, leaf-green and sunlight are necessary 

 conditions. 



'2. Starch is a very common substance in 

 plant tissues. It is one of the chief forms in 

 which plants store up reserves of food to be 

 used on some future occasion when greater 

 demands arc made for food than can be sup- 

 plied by the assimilation of the moment. In 

 the production of fresh shoots from yams or 

 potatos or in the uci mination of seeds, a large 

 amount of growth goes on, entirely at the 



