190 VEGETABLE PHYSIOLOGY 



with the cell-protoplasm. It is contained in the substance 

 called nuclein to the extent of about 6 per cent. The 

 nuclein is apparently chiefly in the chromatin substance 

 of the nucleus. Phosphorus is also a constituent of some 

 proteids, and is probably present in the enzymes which 

 are concerned in the true digestive processes of the plant. 

 It occurs in chlorophyll also, according to Hoppe-Seyler, 

 whose analysis of this pigment has already been quoted 



(page 158). In a few plants phos- 

 phorus is temporarily stored in the 

 seeds. Examples are presented by 

 the Brazil nut (Bertliolletia) and 

 the Castor-oil plant (Ricinus), whose 

 seeds contain stores of proteid 

 FIG. 92. CELL OF EICIMJS material in the form of complex 



SEED. CONTAINING FIVE T ,-, , , P , , 



ALEUBONE GRAINS. grams. In the substance of these 



grains there is a small, usually 



round, accumulation of mineral matter composed of a 

 double phosphate of calcium and magnesium (fig. 92), 

 which lies side by side with a crystal-like proteid body. 

 Lecithin, a complex fatty body containing phosphorus, is 

 present in actively growing cells of many plants. 



Phosphorus is absorbed by the plant usually, if not 

 entirely, in the form of soluble phosphates, most frequently 

 a phosphate of calcium. Besides being important as an 

 integral part of the living substance, certain observations 

 tend to show that it materially assists in the construction 

 of proteids. 



The second group of ash constituents includes four 

 metals which are essential to all plants, viz. potassium, 

 magnesium, calcium, and iron. Probably these act only 

 indirectly in the constructive processes, though there is 

 some evidence that they may be integral constituents of 

 living substance. They do not enter into the composition 

 of proteids. 



Potassium is absorbed in a variety of compounds, of 

 which the nitrate and the chloride are the most advan- 



