216 linTANY PABT I 



sense, and especially in the animal kingdom, the word assimilation is 

 used for all nutritive processes by which the nourishment is built up 

 into the substance of an organism. But in Botany the meaning of 

 the term has gradually been restricted, and now by assimilation the 

 assimilation of carbon by means of the chlorophyll granules is 

 specially understood. Moreover, all the further synthetic processes 

 of assimilation are dependent upon carbon assimilation. 



The chlorophyll bodies, however, can only produce organic sub- 

 stances from carbonic acid and water by help of the vibrations of 

 light (PHOTOSYNTHESIS). The chlorophyll apparatus is unable to 

 assimilate in darkness, although all the other requirements are 

 present for active assimilation. Given a source of illumination, 

 either natural or artificial, assimilation commences, and, within 

 certain limits, increases in proportion to the intensity of the effective 

 rays. Unfavourable conditions, such as cold, or the presence of 

 poisonous substances, may inhibit the action of the chlorophyll 

 apparatus. 



The vibrations of the ether perceptible as light supply the energy 

 for the decomposition of carbonic acid and the production of carbon, 

 just as other vibrations, in the form of heat, supply the energy 

 requisite for the working of a steam-engine. A considerable amount 

 of work has to be done in the assimilation of carbon, and on the 

 potential energy thus stored up the vital processes are mainly 

 dependent. Even the force exerted by the steam engine can be 

 referred to the work of assimilation which was performed by the 

 plants whose remains are burnt in the furnace. For in the process of 

 combustion the organic material is oxidised producing carbon dioxide, 

 and the energy which was originally needed to produce the substance 

 of the plants from carbon dioxide is set free. 



Not all light vibrations are equally capable of arousing the 

 assimilatory activity. Just as the rays of different refrangibility 

 differ in their action, both upon the eye and the photographic plate, 

 so they have a different effect upon assimilation. It would be 

 natural to suppose that the chemically active rays, the blue and 

 violet, which decompose silver salts and other chemical compounds, 

 would also be the most effective in promoting the assimilatory activity 

 of the chlorophyll bodies. Exactly the contrary, however, has been 

 shown to be the case. The highly refractive chemical rays have 

 little or no effect on assimilation ; the red, orange, and yellow rays, 

 that is, the so-called illuminating rays of the spectrum, are on the 

 contrary the most active ( 3C ). 



In the red-leaved varieties of green plants, such as the Purple Beech and Red 

 Cabbage, the chlorophyll is developed in the same manner as in the green parent 

 species, but it is hidden from view by a red colouring matter in the epidermis or 

 in deeper-lying cells. In the Red Algae on the other hand the chromatophores 

 themselves have a red colour ; after death this becomes free as a bluish-red pigment 



