PENTOSE SUGARS IN PLANT METABOLISM 



379 



temperature, 28°. It is a very striking fact that although the 

 joints are constantly losing water through transpiration, the 

 water content after about the first month remains fairly con- 



TABLE 7 

 The course of carbohydrate depletion during starvation of Opuntia sp. 



Dry weight 



Total sugars 



Total polysaccharides 



Total hexose sugars 



Hexose polysaccharides 



Disaccharides 



Hexoses 



"Total pentose sugars 



Pentosans 



Pentoses 



Monosaccharides 



Monosaccharides to total polysacchar 



ides 



Total pentoses to total sugars 



Decem- 

 ber 20 



31.50 



22.86 



20.38 



19.74 



17.64 



1.63 



0.62 



2.93 



2.67 



0.36 



0.98 



0.048 

 0.128 



Febru- 

 ary 12 



36. 

 16. 

 14. 

 14. 

 13, 



0. 



0. 



1, 



1. 



0. 



0. 



0. 

 0. 



80 

 62 

 22 

 85 

 ,72 

 72 

 49 

 68 

 33 

 34 

 83 



058 

 101 



March 

 2 



36.20 



13.71 



12.30 



12.25 



11.15 



0.73 



0.45 



1.38 



1.08 



0.30 



0.75 



0.061 

 0.101 



March 

 22 



40.13 



15.23 



14.10 



13.27 



12.41 



0.70 



0.21 



1.84 



1.55 



0.25 



0.46 



0.033 

 0.121 



April 

 20 



40.50 



14.54 



13.52 



12.24 



11.48 



0.55 



0.26 



2.17 



,2.02 



0.15 



0.31 



0.023 

 0.149 



May 

 12 



37.60 



13.52 



12.46 



11.70 



10.87 



0.59 



0.30 



1.72 



1.50 



0.22 



0.52 



0.042 

 0.127 



stant.^" Thus also the proportions of the various sugars to each 

 other maintain a surprising regularity as the depletion proceeds; 

 hexose and pentose sugars are consumed at about the same rela- 

 tive rates (table 7). It is quite evident that not only is there no 

 accumulation of pentoses but these sugars are used up at a 

 very appreciable rate. 



'" Mac Dougal, D. T., E. R. Long and J. C. Brown, End results of the desicca- 

 tion and respiration in succulent plants. Physiol. Res. 1: 289-325, 1915. 



