CHEMICAL COMPOSITION OF PLANTS 35 



evidenced by the presence of glycogen and certain characteristic 

 fractions of the fats and proteins. A full separation of the reserve 

 substances from the active ones, however, is hardly possible, 

 since for their work the active parts of protoplasm continually 

 require reserve substances and, besides the reserves stored in 

 special tissues, each cell contains a certain amount of them. 



Per Cent 



Fats ••■ 17.85 



Lecithin 4.67 



Cholesterol .58 



Mono- and disaccharides 8.06 



Polysaccharides (largely glycogen) 17.02 



Soluble nitrogenous substances 12 . 00 



Proteins (including nucleoproteins) 20 . 65 



Plastin 8.42 



Nucleic acid 3 . 68 



Fats from lecithoproteins 1-20 



Unknown substances 5.87 



Total 100.00 



It is convenient to start the study of the chemical substances 

 forming the plant and of their essential transformations insepa- 

 rably connected with the vital activity of the plant by an examina- 

 tion of the chemical composition of seeds and of the processes 

 of metaboHsm that develop during germination. One of the 

 advantages of seeds for chemical investigations is the presence 

 of comparatively large reserves of sufficiently uniform substances 

 convenient for investigation. On the other hand, completely dry 

 seeds represent dormant parts of the plant, in which all the 

 i chemical transformations may proceed at a very slow rate. 

 That is why there is no danger during the process of isolation of 

 the substances of their undergoing any marked changes by virtue 

 of their vital activity. At the same time, in seeds that have 

 begun to germinate the most important biological reactions 

 proceed so intensely that they are most convenient for quanti- 

 tative studies. Then too, in the beginning of germination, 

 nearly all of the processes are restricted to those of decompo- 

 sition, while later on they are accompanied by synthesis. This 

 permits the study of these processes separately, a procedure 

 very difficult if not impossible in investigating the life activity 

 of adult parts of plants. Similarly convenient subjects for study 

 are presented by other storage organs in plants, which serve 



