
THE PRINCIPLE OF VITAL AFFINITY. 185 
3. It is unnecessary to enter here on the varieties of this amylaceous matter 
which are formed in different vegetables or parts of the same, the cellulose of 
which the cells are formed, the starch, the dextrin, the gum, the inuline, which are 
deposited in different species and in different parts. AJ] these appear to have the 
same simple fundamental composition, consisting almost entirely of carbon with the 
elements of water, and all are formed out of the same compounds and by a 
vital affinity essentially the same; it may be partly owing to some imperceptible 
difference in the relative position of the ultimate atoms, partly to differences in 
the minute quantities of inorganic matter, and of other organic compounds not 
yet mentioned, which enter into their composition, that so many varieties are 
found, not only in these compounds themselves, but in the qualities which they 
present as found in different species of plants, and even in different individuals 
of the same species. In the case of a graft inserted on the stem of an individual, 
or even of a species, different from that which furnishes the shoot, we see that the 
vital affinities of the particles composing the shoot are capable, not only of 
extracting from the nourishing fluid of the stock all the compounds required for 
its development, but of imparting to the living textures formed of those com- 
pounds which they extract, all those peculiar properties of form, of colour, of 
smell, of roughness, smoothness, &c., by which species, and even individuals of 
the same species, are characterized. And when we consider these facts, I ap- 
prehend we must admit that, under the influence of the vital affinities which 
operate in the cells of living vegetables, much more minute differences of com- 
pounds are produced, than can be detected and explained by any chemical ana- 
lysis. 
4. An important question here is, whether the carbonic acid of the air is 
decomposed in the leaves where it is chiefly taken in, the amylaceous compounds 
immediately formed with the help of water, and the oxygen set at liberty, cr 
whether that acid is taken into the juices of the plant, as we now know that 
oxygen is into the blood at the lungs, and gradually decomposed there, letting its 
| oxygen escape gradually, and aiding in the formation of different compounds, 
| besides the varieties of starch. That the latter is the more probable supposition 
| may be inferred, partly from the analogy of the action at the lungs of animals, 
| but chiefly from the fact, that a separation of oxygen is equally required for the 
_ elaboration, which certainly takes places in vegetables, of other compounds, of 
| the varieties of oil, and of protein, which are chiefly deposited in other parts of 
| their structures. 
5. The relations of compounds of this class to sugar demand more special 
_ notice. It seems doubtful whether this is ever the first compound formed; it ap- 
pears in the sap of various plants when the fluids from the soil are ascending and 
| dissolving the starch which had been formed and stored up by the living actions 
_ of the preceding year ; it appears in almost exactly the same circumstances dur- 
VOL, XVI, PART II. SA 
