74 SOME RECENT RESEARCHES IN PLANT PHYSIOLOGY 



tion of pectin by the alkalies and alkaline earths was being 

 carried out, and has come to the author's notice since the 

 foregoing pages were written. 



Haynes employed parapectin derived from limes and 

 lemons, and measured the rate of precipitation of the jelly 

 by the reagents, assuming the latter process to begin when 

 a definite amount of parapectin had been gelatinized. 

 Thus the time required for precipitation to begin in the 

 jelly could be taken as a measure of the rate of gelatmiza- 

 tion of the solution. With this assumption, Haynes found 

 that the reaction could be represented by the equation 

 c 2 /t = k for dilute solutions, where t is the time required 

 for the formation of precipitate, and c is the concentration 

 of the hydroxides of calcium, strontium, or barium. The 

 interpretation of this, according to Haynes, is that the 

 reaction is a chemical one between the pectin, from which 

 hydrogen is eliminated, and the positive ion of the alkali, 

 as follows : 



P-OH + Ba(OH) 2 = P-OBaOH + H 2 O. 



The original paper should be consulted for a complete 

 consideration of this equation, and for details of much 

 interest. It is hard to correlate the changes with those 

 studied by Ball, since both the methods and sources of 

 material were so entirely different. Ball, however, noticed 

 that his stock solution of pectin, which had remained over 

 for four months, in the absence of a sufficient quantity of 

 toluene, gave immediate precipitates with a drop of various 

 laboratory reagents, sodium hydroxide, copper sulphate, 

 ferric chloride, etc. A comparative study of the two 

 methods would be of interest, and in its absence specula- 

 tion does not seem to be profitable. 



