1889.] Carbon by Green Plants from Organic Compounds. 119 



Papers have been published by A. Meyer and E. Laurent* dealing 

 with this question. 



A. Meyer has shown that the leaves of green plants can form 

 starch when supplied with solutions of glucose, saccharon, mannite, 

 inulin, glycerin. E. Laurent has confirmed this observation for 

 glycerin. 



A. Meyer has shown that starch is not formed from solutions of 

 raffinose,t inosite, erythrite, dulcite, trioxymethylene, aldehyde 

 (acetic) ; and WehmerJ that starch is not produced from formic 

 aldehyde or formose.§ 



The method used by these observers || is placing leaves which have 

 been deprived of starch by keeping in the dark in solutions of the 

 substances, and testing for starch after a certain interval of exposure 

 to daylight. 



I have used "culture " experiments, and in most cases removed the 

 starch at first present in tissues, not by keeping in the dark, but by 

 placing in a receiver, the air of which is completely deprived of C0 2 

 by KOH and soda-lime. 



Sachs's method of testing for starch was generally used, but in most 

 cases also supplemented by direct microchemical observations. 



The experiments fall mostly under three headings — 1 



1. Experiments with shoots. 



2. Experiments with entire plants, the carbon compounds being 



supplied to the roots. 



3. Experiments with shoots of " water-plants." 



In all cases the plants or shoots were placed in a " culture liquid " 

 whilst being completely deprived of starch, and then transferred to 

 another portion of the same culture solution to which the carbon 

 compound had been added in known quantity. The " culture liquid" 

 used was composed as follows : — 



Distilled water 100 grams. K£T0 3 0'15 gram. 



MgCl 2 0-10 „ Ca 3 (P0 4 ) 2 0-05 „ 



EeS0 4 0-025 „ CaS0 4 0-05 „ 



* Both in ' Botan. Zeitung,' 1886. Meyer's paper gives an account of previous 

 work on this subject. 



f Details as to constitution of these compounds and their relations to glucoses 

 are given by Tollens, ' Handbuch der Kohlenhydrate,' Breslau, 1886. 



X ' Deutsch. Chem. Ges. Berichte,' vol. 20, p. 2614. 



§ Quite recently Fischer and Loew have independently shown that formose is a 

 complex mixture, but that it contains a small quantity of a true glucose — probably 

 " acrose." Loew states that this polymerisation only occurs with dilute solutions of 

 the aldehyde (' Deutsch. Chem. G-es. Berichte,' vol. 22, 1889, Hps. 3, 4). Compare 

 also on this point Tollens, loc. cit., p. 250 — 252. 



|| Vide ' Botan. Zeitung,' loc. cit. 



