80 PLANT LIFE ON THE FARM. 



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 developmental 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 department 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 undergo 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 migration of these elements has been well 

 studied in the case of the wheat by M. Isidore Pierre, who 

 has conclusively shown that what the leaves lose in these 

 respects is gained by the ear. One important feature of 



