CHEMICAL COMPOSITION OF PLANTS 79 



tion. In exchange, the seedUngs have obtained free energy- 

 necessary for their growth and vital activity. 



The general aspect of metabolism of reserve substances would 

 not be complete without mentioning the metabolism of the 

 mineral substances. An elementary analysis of seeds will show 

 that besides the four essential elements participating in the 

 formation of carbohydrates, fats, and proteins, viz., carbon, 

 hydrogen, oxygen, and nitrogen, they contain a number of other 

 chemical elements. The most important of these are sulphur, 

 phosphorus, potassium, magnesium, calcium, and iron. As has 

 already been stated, some of these elements, viz., sulphur and 

 phosphorus, participate directly in the structure of proteins. 

 Sulphur is present in all protein substances without exception, 

 while phosphorus, or more exactly phosphoric acid, is an indis- 

 pensable part of the proteins of the nucleus. Moreover, sulphur 

 and phosphoric acid play a very important role in the process of 

 respiration, which is very intense in germinating seeds. That 

 is why there are always found in seeds reserves of compounds of 

 sulphur and phosphorus, chiefly as part of the protein molecules. 

 When these protein substances are stored in the form of aleurone 

 grains, there may be observed under the microscope inclusions 

 of phosphoric acid salts, as well as of other salts that have been 

 generally termed '^globoids." During germination, the globoids 

 dissolve. The significance of other mineral elements during 

 germination comes chiefly from the regulatory action of their 

 ions upon the colloidal chemical processes taking place in the 

 cell. The significance of cations has already been mentioned 

 in the discussion of the question of the stability and coagulation 

 of hydrosols. No considerable reserves of different cations are 

 found in the seeds, however; for in natural conditions of germina- 

 tion in the moist soil, the seeds find and absorb sufficient quan- 

 tities of necessary cations from the surrounding medium. But 

 in germinating seeds in distilled water, one may frequently 

 observe sjmiptoms of acute deficiency in mineral cations. In 

 such cases, the addition of necessary salts may be of great 

 significance. 



Since the question of the needs of seedlings for mineral salts 

 is very difficult to separate from the problem of mineral nutrition 

 of mature plants, a more detailed discussion of the subject will 

 be deferred to Chap. VII, where the problem of the significance 



