62 PLANT PHYSIOLOGY 



oxymethyl-sodium-sulphonate, which can readily be broken 

 up at a regular rate into formic aldehyde and acid sodic 

 sulphite. Spirogyra thrives on this diet, but this fact does 

 not justify the conclusion of the experimenters that formic 

 aldehyde is first formed or formed at all by green plants 

 in the photosynthesis of food; it simply proves that Spi- 

 rogyrn is able under the conditions of the experiment 

 to supply itself with carbon from other than the usual 

 source. 



Emil Fischer's hypothesis regarding the formation of 

 sugar ( starch, etc. ) by green plants, * represents the mature 

 ideas of an eminent chemist; it is supported by no experi- 

 mental evidence from physiologists, yet it is not out of 

 place here. " The formation of sugar is accomplished, accord- 

 ing to the plant-physiologists, in the chlorophyll grain, itself 

 composed of optically active substances exclusively. I be- 

 lieve that the formation of a compound of carbon-dioxide or 

 formic aldehyde with these precedes the formation of sugar, 

 and that then the condensation to sugar, because of the 

 asymmetry of the whole molecule, is accomplished asymmet- 

 rically. The elaborated sugar is torn away from the whole 

 (chlorophyll) molecule and then used by the plant for the 

 preparation of its other component organic compounds." 



The elaboration of carbohydrates by the more or less 

 indirect methods successfully followed by chemists, furnishes 

 little more than plausible hypotheses as to how the green 

 plant elaborates them. The chlorophyll apparatus is not 

 identical in structure, probably much less in its operation, 

 in all green plants, and it is not reasonable to suppose that 

 the different substances formed by its operation are all 

 elaborated in the same ways. Formic aldehyde may be an 

 intermediate product in the formation of sugars and starch, 

 and it may not ; it is hard to see how it can be in the for- 

 mation of fats and oils. Aided by the energy absorbed by 

 the lifeless chlorophyll pigments, the living chloroplastids 

 may form definite new molecules by uniting carbon-dioxide 



bildung aus Formaldehyd. Ber. d. Deutch. Bot. Gesellsch., Bd. IX., p. 

 103+, 1891, and Biologisches Centralblatt, Bd. XVII., 1897. 

 * Fischer, Emil. Synthesen in der Zuckergruppe, II. 1. c., p. 8231. 



