4 PLANT LIFE. 



effected constitutes growth as scientifically understood. 

 Food has not the same chemical composition as the organism 

 feeding on it, but the latter possesses the power of chemi- 

 cally breaking up its food, and retaining those portions that 

 are suitable for becoming chemically transformed into its 

 own substance, the surplus passing away as a by-product. 

 Thus it is seen that increase in size is not necessarily 

 synonymous with growth, as when expansion of a substance 

 takes place on the application of heat, or when a piece of 

 alum increases in size when placed in a solution of its own 

 substance. In the last example the alum, in common with 

 all minerals, possesses the power ofattracting to itself matter 

 having the same chemical composition when dissolved in 

 water, but differs from the action of living matter in not 

 being able to induce chemical changes ; that is, no mineral 

 can cause a chemical change to take place in a substance in 

 solution with which it is in contact, even when all the ele- 

 ments it requires are present, appropriate these, and thus 

 add to the bulk of its own substance and retain its original 

 chemical composition. Consequently, although minerals 

 increase in size under favourable conditions, and according 

 to definite laws, they do not grow. 



(2) Reproduction. — No Kving organism retains its individu- 

 alityand continues to live under equally vigorous conditionsfor 

 an indefinite period of time. To realize this sfatement, it is 

 important to remember that life is not the all-dominant force, 

 as considered by some, but rather that its manifestation de- 

 pends as much on complying as exacting, in its relations with 

 the other forces. Every change means the predominance for 

 the time being of some force previously passive or in abey- 

 ance, and life shares these ebbs and flows in common with the 

 other forces ; consequently, leaving out of consideration the 



