THE PLANT AS A WORKING MACHINE 



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. An indian-corn plant with 

 roots, stem, leaves, anil flowers 



Two kinds of flowers are formed, 

 one in the ear (e), from which the 

 silk i .vi protrudes, and the other In 

 the tassel at the tip of the plant. 

 Special brace root* (b.r) are some- 

 times formed 



