THE PRINCIPLE OF VITAL AFFINITY. 185 



3. It is unnecessary to enter here on the varieties of this amylaceous matter 

 whicli are formed in different vegetables or parts of the same, the cellulose of 

 which the cells are formed, the starch, the dextrin, thef/wm, the inuline, which are 

 deposited in different species and in different parts. All 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, 1 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, or 

 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, Avhich 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. 3 A 



