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196 Structural and Physiolovical Botany. 
intelligible by observing those forces which are inherent in plants from. 
the mode of their construction out of cells, as well as from the molecular 
structure of their organised parts. 
Chemical processes in the interior of the growing structure are always 
connected with growth by intussusception, as this process has already 
been described. Thus, for example, the nutrient fluid which forces its 
way into the cells from without by the action of osmose, contains, it is 
true, material for the formation of molecules of a definite chemical 
composition ; but this material is chemically different from the molecules 
which it nourishes. Thus starch-grains are produced out of a fluid 
Which does not contain any starch in solution; the cell-wall is formed 
by the secretion of substances out of the protoplasm which are not 
_ dissolved cellulose ; the colouring matter of the chlorophyll is first 
formed in the interior of the chlorophyll-bodies, &c. Growth by intus- 
susception is therefore connected not only with a continual disturbance 
of molecular equilibrium, but also with chemical processes in the in- 
terior of the growing structure. Chemical combinations of the most 
- various character must therefore take place between the molecules of the 
organised body, and act and react upon one another. | 
It is certain that growth can only take place so long as the growing 
parts of the cell are permeated by atmospheric air, and that the oxygen 
of the atmosphere decomposes the compounds within the organised 
structure.! The formation and evolution of carbon dioxide is therefore a 
necessary accompaniment of growth ; and not only is the equilibrium 
of chemical forces thus being continually disturbed, but heat is also 
necessarily produced, and electrical action may, perhaps, also come 
into play. | 
By the chemical processes which have been partially described in 
detail when treating of nutrition, by the influence of heat, and perhaps 
also by electrical action, forces of considerable magnitude are set free 
in the interior of the plant, which set in motion its smallest particles 
(atoms or molecules), and thus represent a definite amount of work 
within the growing organised body, which is probably often enormous.” 
And herein we have an essential characteristic of all organisation and of 
1 See p. 167, on the process of respiration. 
2 The temperature of dry grains of starch, when they absorb water 
of the same temperature, rises 2° or 3° C.; while boiling water is only 
raised in temperature about 0°'078° C. by a pressure of ten atmospheres. 
Since, as experiment has shown, the rise in temperature on absorption 
depends on an increase in density of the water, these statements will 
give some idea of the enormous force with which the absorption takes 
place. 
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