14 INTRODUCTION TO BOTANY 
coloring substance known as chlorophyll. When the sun shines 
upon the leaf, the chlorophyll absorbs energy from the sun’s 
rays. This energy serves to decompose the water and carbon 
dioxide. The products of this decomposition immediately 
reunite, but into new substances, which, after several chemi- 
cal changes, may become sugar or starch. Sugar and starch 
may be used as food by the leaf, or be carried to other parts 
of the plant and used, or be made into more complex foods, 
as oils or protein foods. It is from foods that plants as well 
as animals de- 
rive the energy 
that makes ac- 
tivity, growth, 
and life itself 
possible. 
A - ie Since water 
ae “and carbon di- 
oxide, the sub- 
stances from 
which a green 
plant thus man- 
ufactures food, 
are substances 
that are not ordinarily regarded as foods for other living things, 
this process is far-reaching in its significance. The storage of 
surplus plant food in seeds (fig. 12), roots, stems, and leaves 
is also most significant, since our food and many of our 
industries depend upon this surplus material. 
12. The flower. In addition to the roots, stems, and leaves, 
flowers are often conspicuous parts of plants. They are the 
structures by means of which seeds are produced. In some 
plants but one kind of flower is produced (fig. 9); in others 
two kinds are formed (figs. 10 and 11). In such a flower as 
that shown in figure 9 the outermost and lowest floral parts 
form the calyx, each part being a sepal; the parts next above 
the calyx constitute the corolla, each part being a petul ; above 
Fic. 9. Diagrams of two flowers 
A, entire flower; B, flower with part of the floral 
structures removed 
