FERTILIZATION. 67 



When the unravelling is completed, the water, gases, and 

 salts resulting from the decomposition of the tree may 

 almost at once pass through a similar cycle, by being again 

 pressed into the temporary service of another tree of the 

 same species as the one into whose composition it was 

 previously incorporated ; or the cycle may be slightly modi- 

 fied by being utilized by a different kind of tree. A yet 

 wider cycle of change would befall our original inorganic 

 matter if, after being fashioned by life into a plant, this 

 plant should be eaten by some herbivorous animal, whence 

 it would rapidly change from plant to animal substance, in 

 turn to find itself once more, on the death of the animal, 

 the same inorganic matter from which it started its cycle of 

 varied chemical and physical combinations. 



The evolution of sex, in addition to the advantage referred 

 to of concentrating the hereditary peculiarities of species 

 within the Compass of a small portion of the plant substance 

 — the seed, also gave directly an enormous impetus to the 

 invigoration and consequent extension of plant life, by 

 rendering possible cross-fertilization, which is amongst the 

 most active of means for heightening variations, and also of 

 mingling such in the most favourable proportions. For the 

 purpose of securing cross-fertilization and at the same time 

 preventing self-fertilization, numberless modifications and 

 developments in phanerogams have been from time to time 

 added; as a rule, colour, scent, and diversity of form met 

 with in the flower have originated for the purpose of aiding 

 this object ; the various forms of inflorescence, or grouping 

 of flowers in clusters, as also the division of labour met 

 with in some forms of inflorescence, well illustrated in 

 composite plants, as the ox-eye daisy {^Chrysanthemum 

 leucanihemum), where the peripheral or ray florets have the 



