UTILIZATION OF PLANT FOOD 37 



of carbon for the proteins, and Inasmuch as formation of 

 carbohydrates depends on light, protein synthesis takes 

 place usually more rapidly in the light. 



31. Transfer of Oil and Protein. — Just as starch is rendered 

 soluble and transported throughout the plant to parts needing 

 new material, so are oils and proteins changed. Lipases and 

 proteases are not confined to the seeds. They exist anywhere 

 in the plant that oil and protein splitting is essential. Oils 

 are hydrolyzed to glycerine and fatty acids, the latter to 

 soap just as in the seed. Proteins are hydrolyzed to simpler 

 compounds such as albumoses, peptones, amides, etc. It 

 is not known whether the breaking down of proteins goes 

 through the same changes in reverse order as the synthesis, 

 but possibly it does. The course of dissolved oils and pro- 

 teins through the plant is the same as that of dextrose, or 

 dissolved carbohvdrates. 



32. Functions of Carbohydrate, Oil, and Protein. — For 

 respiration and the consequent production of energy in the 

 plant, carbohydrates are principally used. Oils and proteins, 

 however, may serve this purpose. For the manufacture 

 of cell walls, carbohydrates are employed. As was seen in 

 Section 24, soluble material like dextrose is changed to 

 cellulose. For the manufacture of protoplasm, and as 

 storage material for the crop of the following year, all three 

 kinds of material are important. 



33. Protoplasm. — The substance which plays the most 

 active role in all of these chemical changes, and which must 

 be constantlv renewed in old cells and increased for new 

 cells, is protoplasm (Fig. 4, p). Its appearance is not the 

 same in different cells but in general it is a more or less soft, 

 spongy, slimy, granular mass, practically colorless, and sus- 

 pended in water. Embedded in it are always the nucleus 

 or real seat of life, and varying with conditions, chloroplasts 

 or chlorophyl cells, particles of starch, droplets of oil, and 

 many other substances of more or less temporary nature. 

 The approximate chemical composition of the dry matter 

 of protoplasm is as follows : 



50 to 66 per cent, proteins. 



25 to 17 per cent, oils and carbohydrates. 



