112 A TEXTBOOK OF BOTANY [Ch. Ill, 13 



mentioned, namely, a considerable quantity is consumed 

 in respiration, whereby energy is set free for the work of 

 the plant. This important subject will find treatment in 

 the next chapter, along with plant growth where its mani- 

 festations are plainest. There, also, will be traced the final 

 fate of all the plant substances after they have served their 

 functions, or played their other respective parts, in the life of 

 the plant. 



Thus all of the substances constituting the plant body, — 

 the skeleton, foods, living protoplasm, and secretions, and 

 also the materials from which is derived the energy by which 

 plants do their work, — are built up from the photosynthetic 

 sugar, either by direct transformations thereof, or with cer- 

 tain small additions from a few mineral substances taken by 

 the roots from the soil. Upon these materials made by 

 plants all animals are dependent for their food, both that 

 from which they construct their bodies, and that which 

 yields the energy for their work. Thus the importance of 

 the photosynthetic sugar, of the green leaves, and of the 

 photosynthetic process becomes abundantly clear. 



