The Food of Plants 51 
that are needed for 
building proteins, rapid 
growth in a plant is not 
possible. 
The proteins can be 
made in any living part 
of the plant; but the 
materials of which they 
are built are most abun- 
dant in the leaves, and 
they are manufactured 
in larger amounts in the 
leaves than in other 
parts. From the leaves 
they may be carried to 
other parts of the plants 
for storage or for the 
immediate use of the 
cells in those parts. (a 
Materials necessary Fic. 35. The gardeners are appropriating 
for life and manufacture the food that the plants have made for 
themselves. 
of food in green plants. 
Ten chemical elements are necessary for the life and 
_ growth of a green plant. Of these elements, oxygen, 
‘carbon, and hydrogen are used in largest amounts. 
The oxygen used in respiration is secured chiefly from 
the air; that used for building purposes comes from 
water and carbon dioxid. The carbon is obtained in 
the carbon dioxid taken in from the air. The hydro- 
1 These ten elements are carbon, oxygen, hydrogen, nitrogen, sulfur, 
phosphorus, potassium, calcium, magnesium, and iron. 
