THE CONSTITUENTS OF THE ASH OF PLANTS 177 



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 

 proteins, 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 144). In a few plants phos- 

 phorus is temporarily stored in the 

 seeds. Examples are presented by 

 the Brazil nut (Bertholletia) and 

 the Castor-oil plant (Bicinus), whose 

 seeds contain stores of protein 

 material in the form of complex F*. 90. CELL OP KICINUS 



SEED, CONTAINING FIVE 



grams. In the substance of these ALEUKONE GKAINS. 

 grains there is a small, usually 



round, accumulation of mineral matter composed of a 

 double phosphate of calcium and magnesium (fig. 90), 

 which lies side by side with a crystal-like protein 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 assists materially in the construction 

 of proteins. 



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 proteins. 



Potassium is absorbed in a variety of compounds, of 

 which the nitrate and the chloride are the most advan- 

 tageous. The part which it plays is not at all well under- 



12 



