THE FOOD OF PLANTS 125 



different from that of their green relations that it has a 

 totally distinct mode of nutrition. 



In the flowering plants we find a stage of their life in 

 which the nutritive processes approximate very closely to 

 those of the group last mentioned. When the young sporo- 

 phyte first begins its independent life when, that is, it 

 exists in the form of the embryo in the seed its living 

 substance has no power to utilise the simple inorganic com- 

 pounds spoken of. Its nutritive pabulum is supplied to it 

 in the shape of certain complex organic substances which 

 have been stored in some part or other of the seed, some- 

 times even in its own tissues, by the parent plant from 

 which it springs. When the tuber of a potato begins to 

 germinate, the shoots which it puts out derive their food 

 from the accumulated store of nutritive material which has 

 been laid up in the cells of its interior. Considerable growth 

 and development can take place without the access of any 

 of the inorganic substances which the parent plant was 

 continually absorbing. Fleshy roots, corms, bulbs, and all 

 bodies which are capable of renewed life after a period of 

 quiescence, show us the same thing ; the young shoots 

 emerging from any of them are not fed upon simple inorganic 

 bodies, but upon substances of considerable complexity, 

 which they derive from the tissues of the structures from 

 which they spring. 



In adult plants of the most considerable complexity we 

 find instances of the same thing, though in these cases it 

 is generally rather more difficult to determine it ; the 

 living substance is nourished by materials which have 

 been constructed by it and stored at various places in its 

 tissues till their consumption has been called for. 



What, then, are these substances which, in the strict 

 sense, constitute the food of plants ? We can ascertain 

 what are necessary by inquiring what are the materials 

 which are deposited in the seed for the nutrition of the 

 embryo during the process of germination. This process 

 is the most favourable for the elucidation of this point, 



