I 2 2 Carbon A ssimilation. 



values in the same samples is suspicious, and the most likely 

 explanation is that in some cases, at any rate, they are apparent 

 maxima and minima, due to errors in sampling. This is especially 

 so in the case of the maxima at 2 p.m., which appear owing to the 

 minnna at 4 p.m. Thus, if the minimum value found for hexoses in 

 this case were increased hy 7%, the minimum on the hexose curve 

 would disappear, and we have already cited the instance in which 

 the hexose content of two samples collected under similar conditions 

 differed by 6%. 



It seems reasonable to conclude from Davis, Daish and Sawyer's 

 figures that the hexose and sucrose in the leaf increase during the 

 day and then gradually decrease during the night. The maximum 

 in these sugars in the middle of the night, at 2 a.m., is extremely 

 difficult to account for on any other ground than error in sampling, 

 for the leaf manufactures no fresh material, and yet the total 

 carbohydrate in the leaf (pentosan, sucrose, hexose and pentose) has 

 increased from 19-53% to 22-13% of the total dry matter of the leaf 

 according to Davis, Daish and Sawyer's complete analysis. These 

 authors suppose this increase is due to the breaking down of a 

 water soluble gummy substance in the leaf into carbohydrates. 



The relative variations in sucrose content are similar to those 

 in August, although the percentage of sucrose is more than twice 

 as great. The total hexoses present is about the same amount by 

 weight as sucrose, and is much more than is present earlier in the 

 season. 



The pentose content varies little throughout the day ; it appears 

 to diminish somewhat during the night. 



The results obtained for the last stage of growth are similar to 

 those obtained for the intermediate stage. They are shown 

 graphically in Pig. 16. As before, the sugar content is greater 

 duiing the day than during the night. In this case, hexoses and 

 sucrose show two maxima during the night, at 7 or 9 p.m. and at 

 3 a.m. As we have already indicated, the data furnished by the 

 experiments of Davis, Daish and Sawyer are insufficient to enable 

 us to judge whether such night maxima in sugar content actually 

 exist in mangold leaves, or whether their appearance in the curves 

 is simply due to a sampling error. 



The results obtained by Davis, Daish and Sawyer in regard to 

 carbohydrates in the mangold leaf may be summarised as follows : — 



(i.) All the sugars in the leaf increase in quantity from the first 

 to the final stage of growth. 



