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. 



Since water 

 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 petal ; above 



A ' * B 



FIG. 9. Diagrams of two flowers 



A, entire flower ; B, flower with part of the floral 

 structures removed 



