620 CHEMICAL PROCESSES IN THE PLANT. 



is taken into account, the fact becomes the more remarkable that this enormous 

 quantity of carbon is derived from the carbon dioxide of the atmosphere of which 

 it forms on the average only about 0-04 per cent. It is only the cells which contain 

 chlorophyll — and only under the influence of sunlight — that have the power of de- 

 composing the carbon dioxide taken up by them, and at the same time of setting 

 free an equal volume of oxygen, in order to produce organic compounds out of 

 the elements of carbon dioxide and water, or in other words to assimilate. It is 

 very probable that under these circumstances carbon dioxide loses only one-half its 

 oxygen, while the other half of the oxygen which is exhaled is derived from the 

 decomposition of water. 



The fact is unquestionable — partly established by direct researches on vege- 

 tation, partly inferred from the circumstances under which many plants live in a 

 natural condition — that most plants which contain chlorophyll {e.g. our cereal crops, 

 beans, tobacco, sunflower, many saxicolous Lichens, Algae, and other water plants) 

 obtain the entire quantity of their carbon by the decomposition of atmospheric 

 carbon dioxide, and require for their nutrition no other compound of carbon from 

 without. But there are also plants which possess no chlorophyll and in which there- 

 fore the means of decomposing carbon dioxide is wanting ; these must absorb the 

 carbon necessary for their constitution in the form of other compounds. But since 

 plants destitute of chlorophyll are either parasites or saprophytes, they absorb their 

 carbon in the form of organic compounds which have been produced by other 

 plants that contain chlorophyll with decomposition of carbon dioxide. Parasites 

 draw these products of assimilation directly from their hosts, while saprophytes 

 (as Neottia Nidus-avis, Epipogiiim G??iehm, Corallorhiza innata, Monotropa, many 

 Fungi, &c.), make use for the same purpose of the materials of other plants which 

 are already in a state of decomposition. Even the food of Fungi which are para- 

 sitic in and on animals is derived from the products of assimilation of plants 

 containing chlorophyll, inasmuch as the whole animal kingdom is dependent on 

 them for its nutrition. The compound of carbon originally present on the earth 

 is the dioxide, and the only abundantly active cause of its decomposition and of 

 the combination of carbon with the elements of water is the cell containing chlo- 

 rophyll. Hence all compounds of carbon of this kind, whether found in animals 

 or in plants or in the products of their decomposition, are derived indirectly from 

 the organs of plants which contain chlorophyll. 



Hydrogen is present, equally with carbon, in every organic compound ; in 

 consequence however of the smallness of its combining equivalent, it falls far 

 below it as a percentage constituent of the weight of the dried substance of 

 plants. As has already been mentioned, the hydrogen of the plant is probably 

 derived from the decomposition of water in cells containing chlorophyll in the 

 presence of sunlight. It enters into combination with the carbon oxide (CO) simul- 

 taneously presented to it by the reduction of the carbon dioxide \ Only a very small 



• [The abstract of Adolph Baeyer's paper on the Chemistry of Vegetable Life in Journ. Chem. 

 Soc. 1871, pp. 331-341, should be consulted. It is shown to be probable that chlorophyll fixes 

 carbon oxide just as hemoglobin does. When sunlight falls upon chlorophyll which is surrounded 

 by carbon dioxide, that compound seems to suffer the same dissociation as at high temperatures, 



