120 



Carbon Assimilation. 



the second series of these workers, measured a fortnight later in 

 the season, the proportion of pentosan is exactly the same as at the 

 earlier period, while the proportion of matter insoluble in alcohol 

 has actually decreased from about 60% to 50%. Nor is there any 

 better evidence for the second alteinative, for at this intermediate 

 stage, wiiere the measurements were taken before and after sunrise, 

 the results obtained show actually a slight increase of these 

 substances after sunrise. The most reasonable explanation is 

 therefore that the differences recorded are simply within the range 

 of experimental error. Similar considerations apply to the variations 

 in the pentose content. 



lO 



2 RM. 



6 Su.T(v- 



5tt 



lO 



2 an 



1T.se. 



Fig. 14. Variation in Content of Various Carbohydrates in the leaf of 

 Mangold during 24 hours, Aug. 26—27, 1913 (After Davis, Daish and Sawyer). 



It is indeed regrettable that Davis, Daish and Sawyer give no 

 data which enable one to judge the likely limits of error of their 

 determinations. They do indeed, under the heading " Probable 

 Error of the Analyses and Methods of Sampling," show that the 

 reduction method and optical rotation method give values for sucrose 

 which differ by about 20%, and they also give the analyses of hexoses 



