CHAP. T.] PLANT ARCHITECTURE. 3 



liarity of living bodies, whether plant or animal, is the 

 power of chemically decomposing these food substances, 

 re-arranging the constituents into the required chemical 

 compounds, and rejecting the useless surplus. As already 

 stated, one use of food is to enable the individual to grow 

 or increase in size, a second use is that of replacing 

 worn out portions of the body, the result of work done ; 

 and after the full growth has been attained, the latter 

 function of food is the most important one. In addition 

 to the above important uses of food, it is known that 

 during the physical and chemical changes undergone by 

 the food material previous to its assimilation or conver- 

 sion into the substance of the body, various forces are 

 generated, as heat, electricity, etc., which may be con- 

 sidered as forms of energy that are factors in the complex 

 force called life. 



An illustration of change produced chemically on 

 carbonic dioxide (C0 2 ) and water ('H 2 0) by plants in 

 the formation of starch (C 6 H I0 5 ), will give some idea 

 of the manner in which the raw food material is mani- 

 pulated and re-arranged, and also how bye- products are 

 formed. 



6 CO, X 5 H,0 = C 6 H I0 5 + 60 2 . 



(Carbonic dioxide.) (Water.) (Starch.) (Oxygen.) 



The above chemical equation means that the raw food 

 materials, carbonic dioxide and water, are taken into the 

 plant in the proportion of six of the former to five of the 

 latter, and under favourable conditions become chemically 

 re-arranged into one part of starch, the substance re- 

 quired by the plant for its own use in building up its 

 tissues, and there remains as a surplus a certain amount 

 of oxygen which is restored as such to the atmosphere. 



