SOLUTION AND FIXATION OF HIOOOLLOIDS 



135 



Strips equivalent to 200 sections with a surface of 2520 sq. 

 mm. were now placed in beakers of distilled water, 10 cc. to 

 each section 12 sq. mm., for a period of twenty-four hours at 

 the same temperature. The evaporation of the water showed 

 0.2570 gram of material had been dissolved from the plates or 

 sections which weighed 1.6731 gram at the beginning, which was 

 equivalent to about 15%. This proportion is to be contrasted 

 with the 7% of the soluble material dissolved from sections of 

 Opuntia allowing for the non-soluble cell-walls. 



Another series of swellings and extractions was made with 

 sections of biocolloids consisting of 8 parts agar and 2 parts 

 gelatine, which were heavier, having a thickness of 0.38 mm. 

 The swellings were as follows at 16°C. 



Strips of this material weighing 1.0316 gram with a surface of 

 2542 sq. mm. were placed in water at temperatures as above for 

 twenty-four hours and when this was evaporated a residue of 

 0.1865 gram was found, which was equivalent to about 18% 

 of the original. Most of this and of the material dissolved from 

 agar sections in all probability is derived from the surface layer 

 of the material as both gelatine and agar are so nearly non- 

 diffusible as to render their extraction from the interior of the 

 section all but impossible. 



A test was arranged to estimate the relative amount of 

 material which might be extracted from plant tissues by a treat- 

 ment which would parallel the immersions used in obtaining 

 swelling measurements. Sections of joints of Opuntia have 

 been used extensively in work on swelling and in order to obtain 

 sufficient material 24 of the customary size for testing under 

 the auxograph were placed in 250 cc. of water at temperatures 



