1 0 Mr. D. Thoday. Experimental Researches on [June 1 1 , 



uncertainty as to its composition, and hence as to tlie amount of carbon 

 dioxide which it represents. 



The fact illustrated by the analyses, that the increase of dry weight 

 corresponding to a given gain of carbon may be less than if it were all 

 composed of starch, justifies the use, in this investigation, of the starch 

 equivalent of the gain of carbon in preference to the carbohydrate 

 equivalent as calculated by Brown and Escombe's " carbohydrate factor," * 

 which would have given a still higher value. 



Brown and Escombe arrived at this factor, for reducing carbon dioxide 

 absorbed to its equivalent gain of dry weight, from data in Brown and 

 Morris' determinations of the relative amounts of starch and various sugars 

 present in leaves of Tropceolum majus after vigorous assimilation. Besides 

 leaving out of account that Brown and Morris did not determine the increase 

 in sugars and starch in these experiments,t it does not allow for the probable 

 accumulation of substances other than carbohydrates. 



In particular there is evidence that proteid formation occurs in assimi- 

 lating leaves.| Saposchnikoffs researchesj are of especial interest in the 

 present connection. He experimented with leaves assimilating normally, 

 and, using the half-leaf method, determined the dry weight, carbohydrates, 

 and proteid of the same portions of leaf material. His figures indicate that 

 the increase in proteid may account for a considerable percentage of the 

 increase of dry weight. 



Since proteids contain a greater percentage of carbon than even starch, 

 the total increase in dry weight must be less than if no proteid were formed 

 at all. The " proteid factor " analogous to Brown and Escombe's carbo- 

 hydrate factor (= 0-64) is about 0"54. Taking their carbohydrate factor for 

 the carbohydrates themselves and supposing that the increase of proteid 

 were equal to one-third of the increase in carbohydrates, as was the case in 

 some of Saposchnikoffs experiments,! the true " dry- weight factor " would be 

 O'Gl, or practically equal to the "starch factor." 



Tiie true factor may vary considerably with conditions. One of 

 8a])oscIinikoflrs experiments§ indicates that, given (1) a comparatively dull 

 * Loc. cit., p. 43. 



t Brown and Morris, "Chemistry and Physiology of Foliage Loaves," ' Jouni. CLeni. 

 See.,' vol. 63, 'Trans.,' 1893, p. ()04. 



I Cf. Menze, loc. cit. ; Crai)()vvicki, " Eivveissbildung iu den chloropliyllfiihieiulen 

 rrtanzen,^' ' Bot. Cent.,' 1889, vol. 3!>, p. .'i.'iG ; Saposehnikoll', " Eiweissstofl'c iind Kohle- 

 liydrato der griiiicn Hliitter als As.siniilationsproduete," 'Bot. Cent.,' 1895, vol. 03, p. 24G ; 

 Zaleski, " P^iweiHshil.lung," ' Ber. d. D. Bot. Ges.,' vol. 15, 1897, p. 536; Palladin, 

 " Influence de la Liiniiuio sur la Formation des Matierea prot6iques actives et sur I'Energie 

 de la HcHpiralion des Parties verte.s des v6g6taux," 'Eev. g6n. de bot.,' vol. 11, 1899, p. 81. 

 Lor. cit., p. 247. 



