PENTOSE SUGARS IN PLANT METABOLISM 



377 



rain, thereafter the dry fore-summer conditions set in. The 

 effects of these periods of rainfall on the relative sugar content 

 and especially on the pentoses are striking. Changes in temper- 

 ature also affect the equilibrium, and — as separate experiments 

 have shown — in such a manner that at higher temperatures the 

 proportion of monosaccharides is reduced in favor of the poly- 

 saccharides. However, this applies particularly to the hexose 

 sugars, the effect of temperature on the pentose-pentosan equilib- 

 rium is slight. 



TABLE 5 

 Seasonal variations in sugar content of Opuntia sp. 



Dry weight. . . 



Total sugars.. 



Total hexose 

 sugars 



Total pentose 

 sugars 



Pentosans 



Pentoses 



Total pentose 

 sugars to 

 total sugars . 



Total hexose 

 sugars to 

 total sugars . 





36.38 

 20.03 



10.45 



9.26 

 9.04 

 0.20 



0.462 



0.522 



3 



16.45 

 13.24 



8.60 



4.39 





19.66 

 18.44 



8.83 



9.08 

 8.86 

 0.24 



0.332 0.492 0.524 



0.650 



J3 

 O 



20.30 

 20.90 



9.32 



10.95 



10.47 



0.48 



X! 



S 



o 



> 



o 



0.479 



0.446 



23.05 



18.75 



5.50 



12.50 



11.35 



0.82 



0.667 



0.293 



30.10(?) 

 18.95 



7.90 



10.45 



10.10 



0.35 



0.551 



0.417 



C3 

 3 

 C 



22.20 

 19.10 



14.95 



4.73 

 4.40 

 0.43 



0.248 



0.783 



3 

 u 



22.33 

 21.32 



14.90 



6.07 

 5.51 

 0.65 



0.283 



0.698 



19.50 

 28.05 



22.16 



5.55 

 4.75 

 0.82 



0.198 



a 



24.30 

 32.40 



22.70 



9.15 



8.68 

 0.48 



0.283 



0.7910.702 





25.25 

 .30.15 



17.08 



12.34 



12.17 



0.16 



0.409 



0..567 



It was possible to reproduce experimentally the effect of the 

 water content on the pentose sugars. Two sets of Opuntia 

 joints, taken from the same plant, under identical conditions 

 were placed in a dark room at constant temperature, 28°. One 

 set (A) was kept with the base of the joints in water, the other 

 set (B) was kept dry; the experiment continued for a month. 

 (A) produced a few small roots, 5 to 10 cm. long, the water was 

 tested from time to time, but not a trace of sugar could be de- 

 tected. The results are given in table 6. 



