EFFECT OF TEMPERATURE ON THE CARBOHYDRATE-CONTENT. 61 



VII. EFFECT OF TEMPERATURE ON THE 

 CARBOHYDRATE-CONTENT. 



The influence of temperature on the carbohydrate-content of plants such 

 as the platyopuntias is, of course, the summation of the effect of this factor 

 on a variety of activities. In order to eliminate photosynthetic activity in 

 the tests, the plants were kept in the dark. In general the experiments were 

 carried out in the same manner as those described in the preceding section. 

 For each test a number of joints of the same age were taken from a single 

 healthy plant; one set, usually seven joints, was immediately analyzed, 

 while other sets were subjected to experimental conditions. Whether the 

 increase of disaccharides and monosaccharides is the result of the effect of 

 lower temperatures on certain enzyme actions, or whether this merely repre- 

 sents an accumulation of these sugars due to the reduced respiratory activity, 

 it is difficult to establish quantitatively. In considering the effect of tem- 

 perature on the seasonal variations of the carbohydrates in the cacti, it must 

 be borne in mind that during the warm seasons the high temperatures are 

 maintained for a long duration. It is this factor which must be of special 

 importance in applying the thermolabile properties of the enzymes to the 

 present problem. Relatively high temperatures may be borne by many 

 enzymes for short periods, but when such temperatures are maintained for 

 longer periods rapid inactivation ensues. Davis 1 has shown that maltase in 

 plants is greatly reduced in activity and finally destroyed at temperatures 

 above 50. From the records of McGee on the temperatures in cacti, 

 already referred to, it is .evident that these plants during the summer attain 

 35 and higher, and that these temperatures are maintained during the day 

 for 8 to 10 hours. A temperature of 50 within the plant is not at all 

 uncommon. Such conditions may persist daily for 5 months. 



An indication of the effect of temperature on the rate of respiration may 

 be gained from the following experiment. A number of similar joints were 

 taken from the same plant in July and divided into three lots. 



TABLE 26. 



It is evident that B, which, as the following analysis shows, had increased 

 in both hexose and disaccharide content even at 28, evolved considerably 



1 DAVIS, W. A. The distribution of maltase in plants. Exp. Sta. Record, 35, 413, 1916. 



