NATURE 



557 



THURSDAY, APRIL 15, iS 



DOES CHLOROPHYLL DECOMPOSE CARBONIC 

 ACID? 



THE recent memoirs of Pringsheim, noticed in Nature, 

 vol. x\i. p, 85, by Mr. Vines (" Untersuchungcn 

 iiber das Chlorophyll," July and November, 1879) su g- 

 gest very serious doubts as to the correctness of an 

 inference which has crept, without the explicit consent of 

 botanical physiologists, into the position of a fundamental 

 doctrine of biological science. The recent excellent 

 article in Nature on " Vegetation under Electric Light," 

 together with the discussion which took place at the Royal 

 Society when Mr. Siemens's paper describing his experi- 

 ments on plants under the influence of the electric light 

 was read, tend still further to make it desirable to examine 

 critically the claims which the inference alluded to has on 

 our adhesion. 



The inference in question is this, that the substance 

 known as chlorophyll has the property of decomposing 

 carbonic acid so as to fix the carbon and liberate a portion 

 of the oxygen of that acid when in the presence of sun 

 light. Accordingly it has been said that " Chlorophyll is 

 the hand wherewith the organic world lays hold of the 

 carbon of the inorganic world." 



Vegetable physiologists are, however, careful not to 

 commit themselves to such an assertion with regard to 

 chlorophyll itself. The chlorophyll-grains or corpuscles 

 are particles of protoplasm impregnated with chlorophyll 

 much in the same way as the blood corpuscles and other 

 tissues of animals are impregnated with haemoglobin. It 

 is one thing to attribute the decomposition of carbonic 

 acid to "cells containing chlorophyll," or even to "chlo- 

 rophyll corpuscles," and another thing to pass from 

 such a wide statement to the definite ascription of the 

 C<_ „- decomposing property to the green-coloured sub- 

 stance chlorophyll. 



It is perfectly true that by the method of concomitant 

 variation we are led to a conclusion favourable to the im- 

 portance of chlorophyll in this function. It is only by 

 plants (or animals) containing chlorophyll and only in 

 those parts of plants containing it that C0 2 is decomposed 

 and oxygen liberated. Further, it appears that wherever 

 chlorophyll is present in a living organism (even an ani- 

 mal) exposed to sunlight, the decomposition of C0 2 takes 

 place. But whilst we are thus justified in connecting 

 chlorophyll with the decomposition in question, any con- 

 clusion as to its sole efficiency, and accordingly any 

 notion of a specific chemical activity on its part, is 

 forbidden by two important facts : firstly, that living 

 protoplasm is always present in intimate association with 

 the chlorophyll when the decomposition of CO., is effected 

 (forming the bulk of the chlorophyll-corpuscle) ; and 

 secondly, that chlorophyll extracted from the chlorophyll- 

 corpuscle and put to the test in the absence of protoplasm 

 has hitherto not been shown to possess the power of 

 effecting the specific decomposition sometimes attributed 

 to it. 



Very usually blood-red and leaf-green are placed side 



by side as complementary, not only in colour, but in 



function, the one active in oxidation and the special 



property of the animal, the other active in deoxidation 



Vol. xxi. — No. 546 



and the special property of the plant. The pleasing 

 agreement in difference which these two bodies apparently 

 present has, no doubt, a real basis in fact, but the actual 

 analogies between them have very possibly tempted the 

 speculative biologist a little too far. 1 Both present re- 

 markable and characteristic absorption spectra, both 

 contain iron, both are diffused in the living albuminoid 

 substance of organisms, the one of plants, the other of 

 animal;:. Nevertheless a most important fact is true of 

 hemoglobin, which we have not ground for asserting 

 with regard to chlorophyll, namely, that it can be ex- 

 tracted from the albuminoid substance with which it is 

 associated, and then, when in a pure crystalline state, can 

 be made to exhibit its peculiar property of combining 

 with oxygen and again liberating that oxygen, just as it. 

 does in the living tissues. 



On the other hand, the peculiar property which has 

 been inferred for chlorophyll, namely, that of seizing the 

 group CO from CO s and liberating O under the influence 

 of sunlight, ceases altogether (as far as we know) when 

 the chlorophyll is detached from the living protoplasm of 

 an organism, and no effect of any kind upon C0 2 can be 

 produced by its agency when thus isolated. 



In reference to this objection to the assumed function 

 of chlorophyll, it may be urged that the chlorophyll, when 

 extracted from the chlorophyll-grain, is chemically altered 

 by the solvent (alcohol or ether) used. To this it appears 

 there is a complete answer. By chlorophyll we mean 

 clearly enough the green substance present in the chloro- 

 phyll corpuscles. This substance is green in virtue of .1 

 specific absorption of light, which happens to be of such 

 a nature as to cause definite well-marked bands of 

 absorption in the spectrum of light which has passed 

 through it. The solution obtained by appropriate treat- 

 ment of green leaves gives precisely the same absorption- 

 bands as does the green substance in the plant (the whole 

 series being moved a very little to the blue end according 

 to the known law that absorption-bands travel in that 

 direction when a less dense solvent is substituted for a 

 more dense one). Hence the green substance, to which 

 we have to limit the term chlorophyll, may be inferred to 

 exist unchanged in the solution. 



The persistence of a complex banded absorption spec- 

 trum is, according to a large range of observations on the 

 phenomena of absorption, a distinct proof of the persist- 

 ence of chemical and molecular constitution. Those who 

 are not prepared to arlmit this must, whilst thus disposing 

 of a part of the evidence against the specific activity of 

 chlorophyll, abandon the only evidence we have in favour 

 of the specific activity of haemoglobin, for it is upon the 

 identity of the absorption-spectra of haemoglobin, both in 

 the organism and in the crystalline form, that we have to 

 depend for the inference that the substance which we 

 extract is the same substance as that which circulates in 

 the blood and colours the muscles. 



It cannot, however, be stated that a negative has been 

 directly proved with regard to the supposed C0 2 -decompos- 

 ing property of chlorophyll. It is possible that chlorophyll, 

 when extracted by solvents from the chlorophyll-corpuscles, 

 may yet be shown to possess that property. The solvents 

 themselves may, so long as they are present, exert an 

 inhibitory effect. Whilst ether and alcohol may do so it 

 1 As an example see Letoumeau, "Biology:" Library of Contemporary 

 Science, 1878, p. 97. 



