CHEMICAL COMPOSITION OF PLANTS I S3 



and (ii) the reproductive functions concerned with the produc- 

 tion of new individuals and the maintenance of the species. 



2. Before examining the nutritive processes in detail, it is 

 necessary to learn something about the substances entering into 

 the composition of plants. 



If a fresh plant is dug up from the ground and placed in an 

 oven heated to a temperature a little above that of boiling water 

 (105°-! io° C.) it soon loses weight, the loss being due to the 

 escape of water from the tissues of the plant. By continuing the 

 drying process for some hours, all the water from the cell-sap, 

 protoplasm, and the cell-walls is expelled, and there remains 

 only the solid matter of the plant. 



This residue or dry matter consists of a great variety of 

 chemical compounds, organic and inorganic ; when ignited and 

 burnt it always leaves a small amount of white or yellowish 

 incombustible ash, composed of inorganic compounds, the chief 

 constituents of which have been originally absorbed from the 

 soil by the roots of the plant. 



The following table shows the amounts of water, dry matter, 

 and ash in 100 parts by weight of the seeds, fruits, leaves, and 

 other portions of a few common plants : — 



