THE FOOD OF PLANTS 125 
different from that of their green relations that it hag a 
totally distinct mode of nutrition. 
In the flowermg 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 game 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, 
