10 FUNCTIONS OF THE NITROGEN, 



changes they are prepared and fitted for entering, when and 

 where it is necessary, into the composition of the solid or fixed 

 parts of the plant. Thus the starch of the seed is changed into 

 the soluble dextrine and sugar of the sap of the young plant, 

 and these again into the insoluble cellular fibre of the stem or 

 wood, as the plant grows, and finally into the insoluble starch 

 of the grain, as its seed fills and ripens. 



3. They each exercise a chemical action, more or less distinct, 

 decided, and intelligible, upon the other elementary bodies and 

 the compounds of them which they meet with in the sap of the 

 plant. In regard to some substances, such as the potash, the soda, 

 the sulphuric and the phosphoric acids, this last function appears 

 to be especially important. These substances influence all the 

 chemical changes which go on in the interior of the plant, and 

 which modify or cause its growth. The same is true of the 

 nitrogen which the plant contains. This elementary body, in 

 the form of albumen or some other of the numerous protein 

 compounds which occur in the sap, presides over, or takes part 

 in, almost every important transformation which the organic 

 matter of the living vegetable undergoes. Thus it is always 

 abundantly present where the starch of the seed or of the tuber 

 (as in the grain of wheat or in the potato) is dissolved and sent 

 up to feed the young shoot ; and again when the soluble sub- 

 stances of the sap are converted into the starch of the grain, of 

 the tuber, or of the body or pith of the tree, one or other of the 

 protein combinations is always found to be present on the spot 

 where the chemical change or transformation is going on. 



Besides their general functions, therefore, the several sub- 

 stances found in plants exercise also special functions in refe- 

 rence to vegetable life and growth. Thus nitrogen is most 

 abundant in the sap of young plants, takes part in most of the 

 changes of organic compounds which go on in the sap, and fixes 

 itself as the plant approaches maturity in greatest abundance in 

 the seeds and in the green leaves. 



Potash and soda circulate in the sap, influence chemical changes 

 very much, and reside or fix themselves most abundantly in 

 green and fleshy leaves, and in bulbous roots. 



Sulphuric acid is very influential in all chemical changes, is 



