

ELEMENTARY CONSTITUENTS OF THE FOOD OF PLANTS. 697 



decomposing 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. Parasites draw these products of assimilation 

 directly from their hosts, while saprophytes (as Neottia Nidus-avis, Epipogium 

 Gmelini, 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 parasitic 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 chlorophyll. Hence all 

 compounds of carbon of this kind, whether found in plants or in animals or in 

 the products of their decomposition, are derived directly or 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 probably enters into combination with the carbonic 

 oxide (CO) simultaneously presented to it by the reduction of the carbon dioxide ^ 



* [From the researches of Moll it appears that the roots take no part in supplying the plant 

 with carbonic dioxide (Moll, Die Herkunft des KohlenstofFs der Pflanzen, Arb. d. bot. Inst, in 

 Wiirzburg, II. i, 1878).] 



2 [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 haemoglobin does. When sunlight falls upon chlorophyll which is surrounded 

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

 oxygen is liberated and carbon oxide remains combined with the chlorophyll. The simplest reduction 

 of carbonic oxide is to formic aldehyde; it need only take up hydrogen, CO + H2 = COH2, and under 

 the influence of the cell-contents, just as by the action of alkalies (which Butlerow has shown to be 

 the case), the aldehyde is transformed into sugar.] 



