1909.] 



Vegetable Assimilatioti and Respiration. 



11 



light so that the rate of formation of carbohydrates may not be great, and 

 (2) an abundant supply of nitrates, practically the whole of the increase may 

 take the form of proteid. In another experiment, in which distilled water 

 was supplied to leaves instead of a nutritive solution, there was, if anything, 

 a slight diminution in the amount of proteid present.* 



The following table illustrates the possible range of variation in the weight 

 of substance which might result from a given intake of carbon dioxide : — 



Table giving Weights of various Substances whicli contain 12 grammes of 

 Carbon, i.e. which are equivalent to 44 grammes of CO2. 



Gmmmes. 

 27 



28 -5 

 30 



14—15 



22—24 

 33 



21 -8 

 20-1 



It appears from this table that the error involved in the assumption tliat 

 the whole increase is of the average composition of starch might possibly be 

 large. Fortunately, published experiments show that the substances which 

 usually form the greater part of the increase are limited to those contain- 

 ing 40 to 50 per cent, of carbon, and that several of these are usually 

 present, of differing composition, so that the average composition shown by 

 the increase probably varies within narrower limits. Taking this smaller 

 series of products, the weight corresponding to 12 grammes of carbon varies 

 between 24 and 30. grammes. This means an extreme error, if the "starch 

 factor " is used, of + 3 grammes in 27 grammes, or about 10 per cent. 



Variations of this kind may occur in the same plant under different 

 conditions, and certainly occur in different plants, so that an error is involved 

 in comparative investigations of all kinds, and the results will therefore 

 only be approximate. But, as the analyses show, there is sufficient 



* Loc. cit., p. 247. Since, in assimilation experiments, detached leaves aie usually 

 supplied with distilled water only, a decrease in proteid might be expected from this 

 experiment of SaposchnikofF. The composition of the increase would thus be difl'erent for 

 attached and detached leaves. 



Carbohydrates — 



Starch, CgHioO.; 



Cane sugar ] 

 Maltose ^CioHjoO,, 

 Inulin J 

 Hexoses, CsHioOj 



Ethereal oils, etc. — 

 C,„H,6, CioH.cO, etc.... 



Nitrogenous substances — 



Proteins 



Amino acids — 



Asparagin 



Leucin 



Tyrosin 



