Water Deficit or Unsatisfied Hydration Capacity. 



107 



capacity by swelling, as it swelled a second time to the same amplitude, 

 except in the acid solution. 



Table 83. 



Table 84. 



Table 85. 



Swelling of fresh material implies bursting of cells by combined 

 imbibition and absorption and the consequent escape of the mucilages 

 which would not occur in the hydration of dried sections, and these 

 would consequently, in reswelling, regain their original dimensions, or 

 repeat the first swelling.^ 



That this action depends 

 on the condition of the cell- 

 masses was demonstrated by 

 the fact that another series 

 of sections of the same plant 

 which included the chloro- 

 phyllose layer and the epi- 

 dermis did not show such du- 

 plication of results on the 

 second swelling. The in- 

 creases at 16° to 18° C. were 

 as shown in table 84. 



It would be unsafe to as- 

 sume that such a result is 

 associated only with a chloro- 

 phyll-bearing tissue,as median 

 shces of a second opuntia 

 with a smaller proportion of 

 mucilage gave similar swell- 

 ings at 16° C, as shown in table 85. 



The lessened swelling in this case can not be attributed to the escape 

 of pentosans from bursting cells, and attention naturally is directed 

 to the readily diffusible amino-acids, the presence of which facilitates 

 hydration in a remarkable way. 



The swelling of the pentosan agar, which has been used so widely 

 in the imbibition measurements in connection with growth, would be 



» MacDougal and Spoehr. The solution and fixation accompanying swelling and drying of 

 biocolloids and plant tissues. Plant World, 22: June 1919. 



