68 BOTANICAL GAZETTE. 



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. Recent 

 articles and discussions 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 carbo nic acid so as to 

 fix the carbon and liberate a portion of the oxygen of that acid, when 

 in the presence of sunlight. 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 decom- 

 position of carbonic acid to "cells containing chlorophyll" or even to 

 "chlorophyll corpuscles," and another thing to pass from such a wide 

 statement to the definite ascription of the COo-decomposing property to 

 the green colored substance chlorophyll. 



It is perfectly true that by the method of concomitant variation, 

 we are led to a conclusion favorable to tlie importance of chlorophyll 

 in this function. It is only by plants (or animals) containing chloro- 

 phyll, and only in those parts of the plants containing it that CO2 

 is decomposed and oxygen liberated. Further, it appears that when- 

 ever chlorophyll is present /« a living organistn (even an animal) ex- 

 posed to sunlight, the decomposition of CO.2 takes place. But 

 while we ar^there justified in co7inecting chlorophyll with the decom- 

 position in question, any conclusion as to its sole efficiency, and ac- 

 cordingly any notion of a specific chemical activity on its part, is for- 

 bidden by two important facts: firstly, that living protoplasm is al- 

 ways present in intimate association with the chlorophyll when the 

 decomposition of CO.^ is effected (forming the bulk of the chloro- 

 phyll corpuscle) ; and secondly, that chlorophyll extracted from the 

 chlorophyll-corpuscle and put to the test /// the absence of protoplasm has 

 hitherto nol. been shown to possess the power of the specific decom 

 position sometimes attributed to it. 



Very usually blood red and leaf green are placed side by side as 

 complementary, not only in color but also in function, the one active 

 in oxidation and the special property of the animal, the other, active 

 in deoxidation and the special property of the plant. Nevertheless, 

 a most important fact is true of haemoglobin 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 pecu- 

 liar property of combining with oxygen, and again liberating that oxy- 

 gen just as it does in living tissues. On the other hand the pecu- 

 liar property which has been inferred for chlorophyll, namely, that of 

 seizing the group CO from CO2 and liberating O under the influence 

 of sunlight, ceases altogether [as far as we know] when chlorophyll is 



