THE VEGETABLE CELL. 89 



are. Since the plant is a complex of closed vesicles filled with 

 fluid, the contents of which stand in reciprocal connexion by en- 

 dobmose, this structure alone affords the possibilitj^- of tlie forma- 

 tion of the most varied chemical coiiipouiids. Even if we would 

 suppose a plant to contain a fluid of the same composition in 

 all its cells, this equilibrium could not last a moment ; for on the 

 one side the sap in the cells of one organ would acquire more con- 

 sistence through evaporation, and tlicrchy call into existence an 

 opposition toward the otlier cells, while in the cells of anotlier 

 organ endosmose might cause the absorption of a thinner fluid, 

 and thus give lise to a flowing of tlie sap from this organ to the 

 former, — wliich would at once cause a nuiltiforjuity of the compo- 

 sition spreading bhioughout all tlie organs. Wbcn we take into 

 consideration, that on one side ammonia with organic compounds 

 are taken up by the cells, while on the otLer side carbonic acid is 

 decomposed, its caibon appropriated, and its oxygen given out, 

 moreover that the cell-walls act by contact upon the contents of 

 the cells, and that this action again differs according to the differ- 

 ent chemical qualities of the cell-wall and contents, — ^it becomes 

 explicable how the most manifold transformations of cell-contents 

 and the formation of abundance of pi o ducts come to pass in the 

 Vegetable Kingdom, the only limitation that exists being the fact 

 that the elementary substances do not combine together under all 

 conditions. 



This is all correct enough, but it does not advance us one step 

 in the knowledge of the processes of vegetable ixutrition. When 

 we place the contents of all the vessels in a chemical laboratory 

 in a condition of reciprocal connexion, we certainly expect that 

 an innumerable series of chemical processes will result, but what 

 they will be we know not, unless we know what the contents of 

 each vessel consist of, and in what order and under wliat circum- 

 stances the contents of one come into operation upon the contents 

 of another. It is of this that we are ignorant in plants, and so 

 long as it remains uninvestigated, we can only set up more or 

 less probable conjectures. 



These circumstances will be my apology for treating this sub- 

 ject as briefly as possible. 



One of the most general phenomena, since it occurs in all 

 green-coloured plants, is, as we have seen, the absorption of car- 

 bonic acid, and the exhalation of oxygen gas. The experimen'ts 

 of Saussure demonstrate that this process stands in most inti- 

 mate connexion with the formation of organic substances; no- 

 thing seemed easier than to explain this process. The neutral 

 compounds of the plant (sugar, gum, starch, inuline and cellulose) 

 are composed of carbon and the elements of water; it was only 

 requisite to assume that the carbonic acid was decomposed in the 

 leaves, its oxygen given out as gas, its carbon combined with 

 water, which is never wanthig in the plant, and the entire pro- 



