Philosophy of Botany. ^31 



the simple plant upward, to the highest being', man himself, 

 and to fathom the great plan of life by comparison of rela- 

 tions and dififerentiations. 



But the services which the microscope had rendered to 

 scientific botany are not ended in detailing the development 

 of plants ; for the cells, whose form and growth the micro- 

 scope had revealed, are not merely the building stones by 

 whose superposition the body of the plant had been built up ; 

 each cell is also an individual living being. Yes, it is the main 

 living principle in the plant. As far as the tree takes up its 

 nutriment it is the cells of its roots which are saturated with 

 the water, which, concealed, circulates in the soil ; while the 

 tops and branches exhale oxygen at the exposure of the sun- 

 light, for it is the green cells of the leaves which absorb car- 

 bonic acid out of the atmosphere and through the stimulus 

 of light waves convert it into chlorophyll, starch, and other 

 substances, and again emit the oxygen into the air. 



Pending their growth, it is the cells which, stretching and 

 swelling in consequence of the absorption of nutritive fluid, 

 give rise to their multiplication in definite directions for the 

 formation of new organs. 



Should disease attack the plant, the cause lies in the cells, 

 which were disturbed in their normal functions ; and if ulti- 

 mately the plant dies, the extinction of life starts from the cells. 



After all the improvements of the methods with which the 

 experimentative physiology had been advanced, and the rela- 

 tion of plant life to light, heat, gravitation, electricity, and 

 chemical affinities had been so much clearer defined, as it was 

 possible to do a hundred years ago, there never was left out o^ 

 sight the importance of referring it to the life of the cell. 



Moreover, it has been Schwann who, in the year 1838, clear- 

 ly demonstrated that also the course of evolution of every an- 

 imal, and even of man, begins with a simple cell ; that all or- 

 gans of animals are composed of cells, and proceeding from 

 the division of the first cell. Further, that the animal cell is 

 of the same structure with the vegetable cell ; there is but one 

 cell and one life. 



The same way that the mathematician uses to find the value 

 of an unknown quantity by the way of a simple equation, on 



