



134 BOTAXICAL GAZETTE [august 



Thus, for example, instead of the common method of taking 

 the total gross volume of a colloid in a dish or test-tube, the auxo- 

 graph calibrates the action of sections like those of agar, which 

 swell almost wholly in one axis (and a related heterotropic swelling 

 is highly probable in all protoplastic action), and records the con- 

 tinuous rate of swelling. This gives the experimenter exact infor- 

 mation on many features, of which the practical cessation of swelling 

 is one of the most important. Thus some of the records show a 

 swelling at a decreasing but notable rate for as long as 20 days. 

 The termination of the experiment at the end of the second or 

 even the tenth day would have eliminated some of the most striking 

 and important features of the reaction. 



Such continuous records are also necessary in following the 

 action of solutions in which the mass relations are such as to require 

 renewal of the liquids, and in the study of plates in which amino 

 compounds, salts, etc., have been incorporated. Of other features, 

 by no means the least advantageous is the use of the same instru- 

 ment in measuring changes in volume by growth swelling of living 

 and dried cell masses of plants. 



A set of results of swelling of various biocolloids is given in 

 table I, in which the increases, first obtained in percentages of 

 the original thickness of the dried material, are converted into 

 figures relative to the swelling in water which is taken as 100. 



The Ph values were calculated from colorimetric tests after 

 the indicator method perfected by Duggar, 6 soy albumin showing 

 a value of 6 . 2 in a o . 5 per cent solution, Opuntia mucilage 5 . 8 in 

 a 1 per cent solution, cherry gum 5.1 in a 1 per cent solution, 

 acacia gum 5.1 in a 1 per cent solution, and gelatine 5.2 in an 

 8 per cent solution. 



These biocolloids are to be regarded as intimately mixed 

 particles, strands, webs, or globules of pentosans and of proteins, 

 as these substances do not unite and are not mutually inter- 



diffusible. 



material 



& 



D UGG AR 



etermination with biolorical fluids. Ann 



1919. 



Duggar, B. M., Refinements in the indicator method of hydrogen ion determina- 

 tion« Kept. Dept. Bot. Research, Carnegie Inst. Wash. 1919. 





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