132 



Hydration and Growth. 



The extended measurements of the swelling of biocolloids containing 

 sugars, dextrose and sucrose, and of such mixtures in solutions of 

 sugars, show that these have but little influence upon imbibition capac- 

 ity. These results suggest that it is to the variations in the pentoses 

 as represented by the mucilages of the opuntias that we must look for 

 a part of the varying imbibition capacity of these and perhaps other 

 plants as well. 



TABLE 104. Seasonal variations in sugar-content of Opuntia sp. 



The vegetative conditions at the Coastal Laboratory are widely 

 different from those at the Desert Laboratory, at which the above 

 results were obtained. Sections of fresh material at the end of August 

 at the first place showed swellings of 7 to 10 per cent at tempera- 

 tures of 15 to 16 C. This was characteristic of the end of the sum- 

 mer cool and foggy season. Higher temperatures and greater average 

 daily illumination resulted in increased desiccation during August and 

 September, with the result that living sections showed an unsatisfied 

 imbibition capacity of 18 per cent at 15 to 16 C. The method of 

 preparing dried median slices was developed at this time, and these 

 showed swellings of 500 per cent at 15 C. and 570 per cent at 20 C. 

 The total proportion of pentose sugars at this tune was 19.10 per cent 

 as compared with 4.39 per cent at Tucson, calculated on dry weight. 

 Dried sections at the Coastal Laboratory taken at the end of Janu- 

 ary, after 2 months of the cool season but with a fair supply of 

 moisture, were found to swell 300 per cent at 14 to 16 C. A test 

 was also made of sections comprising only the epidermal and chloro- 

 phyllose layers of the same material, and these were found to show 

 an increase of 262 per cent at the same temperature. 



Decrease in swelling capacity is seen to occur in the cool season at 

 Tucson and at Carmel. The composition of the joints in September, 

 representing approximately the condition of the material at both 

 places in October, as determined by Dr. H. A. Spoehr, is shown by 

 table 105. 1 



1 MacDougal and Spoehr. Growth and imbibition. Proc. Am. Phil. Soo., 56: 289. 1917. 



