32 OF LIFE, AND ITS CONDITIONS. 



we seem to have an example in the unusual production of carbonic acid 

 which takes place at the period of flowering, especially in such plants as 

 have a fleshy disk or receptacle containing a large quantity of starch ; and 

 thus, it may be surmised, an extra supply of force is provided for the matu- 

 ration of those generative products, whose preparation seems to be the high- 

 est expression of the vital power of the Vegetable Organism. 



10. The entire aggregate of Organic compounds contained in the Vegeta- 

 ble tissues, then, may be considered as the expression not merely of a certain 

 amount of the material elements oxygen, hydrogen, carbon, and nitrogen 

 derived (directly or indirectly) from the water, carbonic acid, and ammonia 

 of the atmosphere, but also of a certain amount of force which has been ex- 

 erted, in raising these from the lower plane of simple binary compounds to 

 the higher level of complex "proximate principles;" whilst the portion of 

 these actually converted into organized tissue may be considered as the ex- 

 pression of a further measure of force, which, acting under the directive 

 agency of the germ, has served to build up the fabric in its characteristic 

 type. This constructive action goes on during the whole Life of the Plant, 

 which essentially manifests itself either in the extension of the original 

 fabric (to which in many instances there seems no determinate limit), or in 

 the production of the germs of new and independent organisms. It is inter- 

 esting to remark that the development of the more permanent parts involves 

 the successional decay and renewal of parts whose existence is temporary ; 

 the "fall of the leaf" being the effect, not the cause, of the cessation of that 

 peculiar functional activity of its tissues, which consists in the elaboration 

 of the nutritive material required for the production of wood. And it would 

 seem as if the duration of the existence of such temporary parts stands in an 

 inverse ratio to the energy of their action ; the leaves of "evergreens," which 

 are not cast off until the appearance of a new succession, effecting their func- 

 tional changes at a much less rapid rate than do those of "deciduous" trees, 

 whose term of life is far more brief. 



11. Thus the final cause or purpose of the whole Vital Activity of the 

 Plant, so far as the individual is concerned, is to produce an indefinite ex- 

 tension of the dense, woody, almost inert, but permanent portions of the 

 fabric, by the successional development, decay, and renewal of the soft, ac- 

 tive, and transitory cellular parenchyma; and, according to the principles 

 already stated, the descent of a portion of the materials of the latter to the 

 condition of binary compounds, which is manifested in the largely increased 

 exhalation of carbonic acid that takes place from the leaves in the later part 

 of the season, comes to the aid of external Heat in supplying the force by 

 which another portion of those materials is raised to the condition of organ- 

 ized tissue. The vital activity of the Plant, however, is further manifested 

 in the provision made for the propagation of its race by the production of 

 the germs of new individuals ; and here, again, we observe that whilst a 

 higher temperature than that which suffices to sustain the ordinary processes 

 of vegetation, is usually required for the development of the flower and the 

 maturation of the seed, a special provision appears to be made in some in- 

 stances for the evolution of force in the sexual apparatus itself, by the retro- 

 grade metamorphosis of a portion of the organic compounds prepared by the 

 previous nutritive operations. This seems the nearest approach presented 

 in the Vegetable organi.-m, to what we shall find to be an ordinary mode 

 of activity in the Animal. That the performance of the generative act in- 

 volves an extraordinary expenditure of Vital force, appears from this re- 

 markable fact, that blossoms which wither and die as soon as the ovules 

 have been fertilized, may be kept fresh for a long period if fertilization be 

 prevented by cutting off' the stamens before the- bursting of the anthers. 



