78 PLANT LIFE ON THE EABM. 



first season of growth, the leaves collect and form the 

 nutritive matters which are subsequently transferred to 

 the " root," and the store so accumulated is utilized the 

 following season in the formation of flowers and seeds, as 

 before explained. 



Growth, then, in a chemical sense, may be said to con- 

 sist in the absorption of the raw materials for the food of 

 plants development, in a chemical sense, may be taken 

 as including the various transformations which those 

 raw materials undergo to fit them for the nutrition of 

 the plant, or the formation of reserve-materials to be 

 stored up for future use. The history of these develop- 

 mental changes is a matter for the chemist to clear up 

 with the aid of chemical re-agents, used both with and 

 without the help of the microscope. It is in this de- 

 partment of physiology that our knowledge is at present 

 most imperfect. 



Maturation. The foregoing facts and phenomena have 

 been brought to light principally by chemical analysis of 

 the same kind of plant at different times and in different 

 stages of its growth, and particularly by the analysis of 

 different parts of the same plant, some young, some old. 

 In the case of wheat, it was ascertained by Messrs. Lawes 

 and Gilbert that during the five weeks beginning with 

 June 21, there was but little accumulation of nitrogen in 

 the plant, while during the same period more than half 

 the total carbon was accumulated. The building-up 

 process was thus going on more quickly than that of 

 maturation. In this manner it has also been found, not 

 only that the starchy and the albuminous matters under- 

 go changes and disappear from the leaves, but that 

 mineral matters and salts, such as phosphates and salts 

 of potash, which at one stage of growth abound in the 

 leaves, at another time are almost entirely absent from 

 them, but are found in abundance elsewhere. The mi- 



