192 NUTRITION 



A seed provided with this nutritive solution, under suitable 

 conditions (see after), can produce a seedling, which in turn 

 may develop into a plant with flowers and fruit. The plant 

 therefore has every chemical element it requires. 



6. A green plant can manufacture complex organic (carbon-) 

 compounds from simple inorganic food. — The solid matter 

 of a seed, or of the plant derived from it, consists mainly of 

 organic compounds — that is, it consists chiefly of compounds 

 of carbon which readily combine with oxygen. Comparing 

 the seed and the plant, apart from the ^reat increase in the 

 amount of water in the plant, the most marked difference in 

 the composition of the two is the immense addition to the 

 quantity of the organic carbon compounds. Cultivated with 

 the "culture-solution" described, the plant has only inorganic 

 food at its command ; in particular, its carbon-containing food 

 is available only in the form of the carbonic acid (CO 2) present 

 in the air. Animals cannot build up organic compounds from 

 simple inorganic food ; this power is confined to plants. 



