70 SOME RECENT RESEARCHES IN PLANT PHYSIOLOGY 



experiment had to be brought to a close, the curve gave 

 indications of approaching a maximum. One slight ir- 

 regularity during the fifth hour was occasioned by an 

 accidental elevation of the temperature. 



Experiment II., at 14, furnished evidence of the great 

 rapidity of the action at this temperature, and revealed 

 the entirely unexpected attainment of a viscosity maxi- 

 mum followed by a rapid decrease, the two sides of the 

 curve being very similar for a considerable distance. 



The other experiments shown in the graph Nos. III., 

 IV. and VI. were carried out at 21. In the first two 

 of these the .same sap was used, but they were per- 

 formed on successive days, and in No. IV. the sap 

 had been neutralized ; toluene was employed as a pre- 

 servative. No. IV. curve shows much the same form as 

 No. III., but never rises to so great a degree of viscosity. 

 Owing, probably, to the sap being poorer in pectase in 

 No. III., the gelatinization proceeds more slowly than in 

 No. II. Since, however, the temperature is higher, one 

 would expect the action to be more rapid, assuming the 

 quantity of enzyme to be constant. Accordingly, an at- 

 tempt was made to see if the difference was due to the 

 acidity of the sap exerting a retarding influence upon the 

 pectase. 



THE INFLUENCE OF IONS UPON THE MAXIMUM VISCOSITY 

 OF THE SOLUTION. 



To test this point, the sap was rendered neutral to litmus, 

 but in the curve of No. IV. it is shown that the maximum, 

 though reached somewhat sooner than in No. III., is much 

 below it. This seemed to be due to the acceleration of the 

 reverse process occasioned by the increase of 'the metallic 

 ions of the sodium hydroxide added. Such an alteration of 

 the relative rates of the two processes would naturally lead 



