THE PRODUCTS OF PHOTOSYNTHESIS 217 



made a careful study of the carbohydrates in the leaves of the mangold at 

 different times of the day and night and at different seasons. The 

 analyses made during the stage of early growth (August 26-27) show that 

 the hexoses and sucrose increase rapidly after sunrise, reach a maximum 

 at about noon, and decrease gradually until the following sunrise. In 

 this stage the amount of sucrose is greater than that of the hexoses; also 

 the variation in the amount of sucrose is smaller than that of the hexoses. 

 In the second stage (September 10-11) the results of the analyses show 

 very dift'erent conditions. Here the amount of hexoses is greater than that 

 of sucrose, the increase is irregular, reaching a maximum at sunset and 

 decreasing irregularly to the following sunrise. In the third stage of the 

 development of the plant (October 11-12) the hexoses are still in excess 

 of sucrose, both show very irregular increases and decreases. Analyses 

 were also made of the carbohydrates of the leaves of potato plants at two 

 hourly intervals. Here the sucrose is in excess of the hexoses and the 

 former shows a gradual increase from sunrise to 2 P.M. and then a de- 

 crease till sunset, while the hexoses show great variation during the day 

 and night. 



The investigations of Brown and Morris, of Parkin and of Davis and 

 his collaborators have been cited here to illustrate the nature of the evi- 

 dence on which has been based the conclusion that sucrose and not glucose 

 is the first sugar formed in photosynthesis. The same conclusion has been 

 reached by Went,^**^ Perry,^°^ Girard ^°= and others. ^°^ 



The objections which may be raised to this conclusion are varied. It 

 has been repeatedly emphasized that the difficulties associated with the 

 preparation of leaf material for analysis and the execution of the analyses 

 themselves are numerous, and that small errors, as for instance in polari- 

 scope readings, may result in very erroneous conclusions. For this reason 

 the amounts of carbohydrates reported are not always reliable, especially 

 in those cases in which conclusions were drawn from polarimetric read- 

 ings. Xo doubt the contradictory results obtained by different investi- 

 gators are to be ascribed in part to differences in the methods employed 

 and in part to differences in light intensity, temperature and water con- 

 tent to which the experimental i)lants were subjected. There is, more- 

 over, the very serious question as to whether it is justifiable to draw con- 

 clusions as to the kinetics of a series of reactions from the amounts of 

 different substances which are found at any time to be present in the mix- 

 ture. In so complex a series of reactions as that of photosynthesis, in 

 which the total reaction runs from carbon dioxide and water to starch, 

 the number of steps involved is, of course, great. Also, some of the 

 steps comprising this total reaction are reversible ; the polysaccharides 

 may be hydrolyzed to monosaccharides for instance. The conditions under 



"'Went, Jahrh. wiss. Bot., 31, 323 (1898). 

 ^•^ Perry, Compt. rend., 94, 1124 (1882). 

 "'Girard, ibid., 97, 1305 (1883). 



J*** Marcacci, Just Jahresb., 1, 26 (1889). Colin, Bull, assoc. chim. sucr. dist 38 

 331 (1821). 



