EFFECT OF WATER ON THE CARBOHYDRATE-CONTENT. 59 



mass as well as to decrease the water-content. These factors are unques- 

 tionably of great importance to the plant, especially under conditions of 

 restricted water-supply and during starvation. Discussion hereof will be 

 taken up again in a following section. 



Table 22 gives the results of analyses of the three sets of cactus joints. 



The proportional values calculated from table 22 are given in table 23. 



The water-content of the plants kept over calcium chloride was reduced 

 from 81.5 per cent to 77.0 per cent; those kept over water were reduced to a 

 water-content of 81.2 per cent. In both cases there was a decided reduction 

 in total sugars. From the available data it is impossible to tell whether all 

 of this reduction is due to respiration or whether in part it is due to the 

 formation of carbohydrates of the nature of cellulose which are not hydro- 

 lyzed with 1 per cent by hydrochloric acid and hence do not appear in the 

 mass of total sugars. It is a noteworthy fact, however, that the actual 

 percentage of total polysaccharides shows an increase in both cases. There 

 is very little difference in the rates of respiration between the two sets of 

 plants, as is shown in table 24. 



TABLE 24. Rate of respiration in milligrams C0 2 of joints of Opuntia phceacantha 



after being kept in the dark for M days. 



From results given in tables 22 and 23 it is clear that under controlled 

 conditions the comparative values of the carbohydrate-content show that 

 with decreased water-content the monosaccharides exhibit a decrease while 

 the polysaccharides show an increase. Also the pentosans increase with 

 decreasing water-supply. 



TABLE 25. Carbohydrate-content of Opuntia phceacantha as affected "by increase and 

 decrease in water-content. Values given in percentages of the dry material. 



Similar results are obtained when instead of allowing only one set of the 

 cactus joints to lose water, the experiment is so arranged that one set loses 

 water while another exactly similar increases in water-content. This was 

 done by placing one set of seven joints in glass battery jars in such a manner 



