78 



CARNEGIE INSTITUTION OF WASHINGTON. 



CARBOHYDRATE EQUILIBRIUM DURING STARVATION. 



The course of carbohydrate consumption during starvation of joints 

 of Opuntia sp. has been followed through two periods of eight and six 

 months, the joints being kept in the dark, without water, and at con- 

 stant temperature, 28 C°. After about the first month the water-content 

 remains fairly constant. The proportion of the various sugars to 

 each other maintains a surprising regularity as the depletion proceeds ; 

 hexose and pentose sugars are consumed at the same relative rates, 

 indicating clearly the use of the latter. 



Dry weight 



Total sugars 



Total polysaccharides. . . 



Total hexose sugar 



Hexose polysaccharides . 



Disaccharides 



Hexoses 



Total pentoses 



Pentoses 



Pentosans 



Monosaccharides 



Monosaccharides to total 

 polysaccharides 



Hexoses to hexose poly- 

 saccharides 



Total pentoses to total 

 sugars 



Dec. 20. 



p. ct. 



31.50 



22.86 



20.38 



19.74 



17.64 



1.63 



0.62 



2.93 



0.36 



2.91 



0.98 



.048 



.035 



.128 



Feb. 12. 



p. ct. 



36.80 



16.62 



14.22 



14.85 



13.72 



0.72 



0.49 



1.68 



0.34 



1.33 



0.83 



.058 



.036 



.101 



Mar. 2. 



p. ct. 



36.20 



13.71 



12.30 



12.25 



11.15 



0.73 



0.45 



1.38 



0.30 



1.08 



0.75 



.061 



.040 



.101 



Mar. 22. 



p. ct. 



40.13 



15.23 



14.10 



13.27 



12.41 



0.70 



0.21 



1.84 



0.25 



1.25 



0.46 



.033 



.017 



.121 



Apr. 20. 



p. ct. 



40.50 



14.54 



13.52 



12.24 



11.48 



0.55 



0.26 



2.17 



0.15 



2.02 



0.31 



.023 



.22 

 .149 



May 12. 



p. ct. 



37.60 



13.52 



12.46 



11.70 



10.87 



0.59 



0.30 



1.72 



0.22 



1.50 



0.52 



.042 



.027 



.127 



Joints which have been thus starved were found to be capable of 

 rapidly replenishing their food-supply from solutions of dextrose and 

 cane sugar. However, in the sunlight, and even with ample water- 

 supply, the amount of sugar formed by photosynthesis is not enough 

 to equal the consumption, and the joints continue to lose sugar. 



Under anaerobic conditions the rate of sugar consumption inOpuntia 

 sp. and 0. versicolor is slightly higher than in air. However, under the 

 former conditions accumulation of certain products of the metabolism 

 soon causes death. Under normal conditions the amount of alcohol 

 formed at any time in the cacti is exceedingly small, increasing appar- 

 ently with the photolysis of the acids. Alcohol accumulates rapidly in 

 an atmosphere free from oxygen. 



THE PENTOSE SUGARS IN PLANT METABOLISM. 



This group of sugars, present in varying amounts in almost all plants, 

 constitutes at times more than half of the total sugars of the cacti, 

 not only in the condensed form as pentosans, but it has been found 

 that a not inconsiderable portion of the monosaccharides are pentose 

 sugars. However, the greater proportion are polysaccharides and also 

 form a regular component of the products of hydrolysis of starch grains. 



I 



