THE PLANT AS A WORKING MACHINE T 
6. The work of plants. Plants 
must have materials for their 
nutrition just as truly as animals 
do. It does not follow, however, 
that the same kinds of food mate- 
rial are needed or that they are 
secured or handled in ways that 
correspond to those found among 
animals. As a rule, animals eat 
plants or animals that have used 
plants as food. Occasionally, as 
we shall see later, seed plants may 
use animals as food material, and 
it is generally known that such 
plants as bacteria and molds may 
live upon animals. Green plants 
may secure water and carbon 
dioxide, and from them they may 
make foods, such as sugar and 
starch. They may use these as 
food or may combine them with 
other substances and thus make 
foods, such as proteins, that are 
more complex than sugar and 
starch. It is also one of the con- 
spicuous and important facts of 
plant life that much surplus plant 
food is stored in grains and fruits, 
and this stored food may serve 
as nutrient material for man and 
the lower animals. Indeed, many 
people find that their chief inter- 
est in plant life is due to the 
possibility of securing and using 
this surplus stored plant food as 
found in such things as the grains 
Fig. 3. Anindian-corn plant with 
roots, stem, leaves, and flowers 
Two kinds of flowers are formed, 
one in the ear (e), from which the 
silk (s) protrudes, and the other in 
the tassel at the tip of the plant. 
Special brace roots (b.r) are some- 
times formed 
