Oct. 1.1919 Notes on the Composition of the Sorghum Plant 



25 



upper portion of the cane, where respiration is proceeding most rapidly. 

 This fact is in accordance with the view that the excess dextrose is the 

 sugar most available for respiration. That portion of the dextrose which 

 is equal to the levulose represents, of course, the invert sugar portion to 

 be converted into sucrose, 



(4) Development of the constituents of the juice. — Many thou- 

 sands of analyses have been made of the juice of sorghum to show the de- 

 velopment of the various constitutents of the juice, especially the sugars. 

 It would be fruitless to review them here, since in general they all show 

 about the same trend of development — an increase of sucrose up to 

 maturity, a decrease in reducing sugars, a concentration of the juice due 

 to desiccation of the ripe cane, and 

 a slight increase in purity (percent- 

 age of total solids as sugars).^ 



The results of the analyses at 

 this station bring out very similar 

 relations among the constituents 

 of the juice. Since nothing new 

 would be contributed by present- 

 ing all the analyses made at this 

 station, only the work of the season 

 of 1 914 is given (fig. 17). This 

 includes the separate determina- 

 tions for levulose and dextrose, 

 which have not been reported 

 heretofore for sorghum juice during 

 a whole season's development. 

 For the sake of direct comparison, 



the only determinations for starch which were made, which were on the 

 1 91 6 crop in connection with topping experiments, are also included in 

 the graphs. Another fact that should be pointed out is that these 

 analyses were made on cane grown at the northern limit of the sorghum- 

 growing regions of the country and hence form a basis of comparison 

 with cane grown during a longer and warmer season. To make this 

 comparison more apparent. Collier's curves (5, p. i6g) for the average 

 results of analyses of Early Amber cane grown at Washington, D. C, in 

 1 881 , are also given in figure 18. 



One or two significant facts can be pointed out in the curves in figure 17. 

 In the first place, the ratio of levulose to dextrose changes during the 

 progress of the development of the plant. As maturity approaches, the 

 dextrose decreases more rapidly than the levulose. At the same time, 

 the starch increases from about 0.7 per cent to 1.8 per cent. This small 

 amount of starch can not account for the marked decrease in dextrose. 



' It should be pointed out that in sorghiun the standard for purity is the total sugars, whereas in sugar-cane 

 and sugar-beet work it is the sucrose alone. This is because of the fact that in sirup making the total sugars 

 are utilized. 



122503°— 19 4 



STAG E S OF MATURITY 



Fig. 17. — Development of the constituents of the 

 juice of sorghum. (See p. 2 for description of the 

 stages of maturity.) 



