PHYSIOLOGY 197 



this function, for the chlorophyll bodies themselves are the laboratories 

 in which this chemical process, so important for the whole living 

 world, is carried on. From these laboratories is derived the whole of 

 the carbon which composes the organic substance of all living things, 

 plants as well as animals. Animals are unable to derive this most 

 essential element of their bodies from inorganic sources. They can 

 only take it up in organic substances, which have been previously 

 formed in plants. Such plants, also, as are without chlorophyll, as, for 

 example, the Fungi and some of the higher parasitic plants, are 

 dependent for their nutrition upon organic substances previously 

 formed by the chlorophyll bodies of other plants. 



"Within the past ten years it has, indeed, been repeatedly determined that 

 certain nitrifying bacteria have the power of forming a small amount of organic 

 substances from carbonates, carbonic acid, and ammonia. The process by which 

 the organic carbon compound is derived must, however, be altogether different from 

 that of green plants, as the bacteria contain no chlorophyll, and their nutritive 

 activity is in no way dependent upon the light. 



Roots and other organs unprovided with chlorophyll, and also the 

 colourless protoplasm in the green cells themselves, are similarly 

 dependent upon the activity of the chloroplasts. 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 : in the case of the brown and red Algae, on the other hand, 

 the chlorophyll pigment is concealed by a colouring matter, which 

 is contained in the chromatophores along with the chlorophyll. 



The derivation of carbon from carbonic acid and its conversion 

 into organic substances is termed Assimilation. In its broadest 

 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 

 carbon assimilation of the chlorophyll granules alone is understood. 

 Moreover, all the other so-called processes of assimilation are dependent 

 upon carbon assimilation. 



The chlorophyll bodies, however, cannot independently produce 

 organic substances from carbonic acid and water, but require the 

 co-operation of light. The chlorophyll apparatus is unable to assimilate 

 without light, although all the other requirements are present for 

 active assimilation. A definite amount of heat is also naturally 

 necessary for chlorophyll activity, just as for any other vital process. 



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 of ether, in the form of heat, supply the energy 

 requisite for the working of a steam-engine. Not all light vibrations 



