85 Original Articles. [Jan. 
place at the expense of compounds previously generated by the plant 
itself, and stored up in its tissues; of which we seem to have an ex- 
ample 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 maturation of 
those generative products, whose preparation seems to be the highest 
expression of the vital power of the Vegetable organism. 
The entire aggregate of organic compounds contained in the vege- 
table 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 exerted, 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 or- 
ganized tissue may be considered as the expression 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 con- 
structive 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 interesting to remark that the development of the more per- 
manent parts involves the successional decay and renewal of parts 
whose existence is temporary. The “fall of the leaf” is 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 their existence 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 functional changes 
at a much less rapid rate than do those of “ deciduous” trees, whose 
term of life is far more brief. 
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 
extension of the dense, woody, almost inert, but permanent portions 
of the fabric, by the successional development, decay, and renewal of 
the soft, active, and transitory cellular parenchyma; and, according 
to the principles already stated, the descent of a portion of the mate- 
rials of the latter to the condition of binary compounds, which is 
manifested in the largely increased exhalation of carbonic adid 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 por- 
tion of those materials is raised to the condition of organized 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 is usually required for the development of the 
flower, and the maturation of the seed, than that which suffices to sus- 
