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. Hxamples are presented by 
the Brazil nut (Bertholletia) and 
the Castor-oil plant (Ricinus), whose 
seeds contain stores of protein 
material in the form of complex Fic. 90.—Cxi. or Ricmus 
a SEED, CONTAINING FIVE 
grains. In the substance of these ALEUKONE GRAINS. 
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. 
ecithin, a complex fatty body containing phosphorus, is 
abe 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 
