THE COMPONENTS OF PLANTS AND ANIMALS 7 



Phosphorus. Phosphorus is another of the elements essential to 

 plant growth, its chief function seeming to be to aid in the produc- 

 tion and transportation of the proteins. It is found in all parts of 

 the plant but accumulates especially in the seeds. 



Plants may contain more or less phosphorus in the form of phos- 

 phates, especially in their vegetative organs. Even in the latter, 

 however, a considerable share of it is in "organic" combination, while 

 in the seeds but very small amounts of " inorganic" phosphorus are 

 found. The " organic." phosphorus of plants is contained chiefly in 

 three classes of compounds, viz., the phosphatids (37, 38), or so- 

 called phosphorized fats, the nucleo- and phospho-proteins (52, 55), 

 and phytin, the latter being the chief phosphorus compound of seeds. 

 Phytin is a compound of phosphoric acid and inosit and may be split 

 up into these constituents by hydrolysis and also by an enzym found 

 in seeds. 



In the animal, the great store of phosphorus is found in the skele- 

 ton, where it exists, as already stated, chiefly in the form of calcium 

 phosphate. It is also found somewhat abundantly in the soft tissues 

 of the body, of which it is an essential ingredient. Here it seems to 

 exist largely in "organic" combination in the phosphatids and the 

 nucleo- and phospho-proteins. 



Sulphur. Sulphur is taken up by the roots of the plant in the 

 form of sulphates, and when plant or animal substances are burned, 

 more or less of the sulphur which they contain is found as sulphates 

 in the ash. For these reasons, sulphur has been commonly regarded 

 as one of the ash ingredients of plants and animals. As a matter of 

 fact, however, as already pointed out, it is usually as truly an "or- 

 ganic" ingredient as nitrogen or carbon. In particular, it is one of 

 the elements of which the proteins are composed, and seems to exist 

 in the plant and animal chiefly in this form. 



Chlorin. Chlorin is found in plants associated with sodium. 

 It does not seem to be necessary to plant life. In the animal it is an 

 essential element in the gastric juice. 



Small amounts of fluorine and traces of iodin and of manganese 

 and other catalysts also occur, but their specific functions are obscure 

 except that fluorin is an ingredient of the enamel of the teeth. 



2. THE CARBOHYDRATES 



6. Occurrence. Although substances belonging to this 

 group of compounds are found in the bodies of animals, they 

 are especially characteristic of plants. Starch, one of the most 

 familiar of them, is the first visible product of the assimilation 



