68 SOME RECENT RESEARCHES IN PLANT PHYSIOLOGY 



of a liquid such as glycerol. From the fact that small 

 quantities of pectin could give rise to a mass of consider- 

 able consistency, it seemed highly probable that the struc- 

 ture was that of a gel. To test the point experimentally, 

 1 c.c. of 2 per cent/ 3 pectin solution was mixed with an 

 equal volume of distilled water and with 1 c.c. of freshly 

 pressed sap. The solution was then placed in a Hamburger 

 conductivity tube at air temperature, 12'5; its resistance 

 was measured from time to time in the usual manner, but 

 up to the time at which it set to a firm jelly, about two 

 hours after mixing, there was no change whatever in the 

 readings. This furnishes definite proof of the gel struc- 

 ture of the gelatinized pectin. 



THE ACTION OF PECTASE STUNTED BY THE 



VlSCOSIMETER 



To study the action of pectase by viscosity determina- 

 tions, Ball constructed a small apparatus of the Ostwald 

 type. The size of the bulb was such that 3 c.c. of solution 

 sufficed for each experiment, the proportions of the con- 

 stituents being the same as in the conductivity determina- 

 tions viz., 1 c.c. each of 2 per cent, pectin, distilled water, 

 and Syringa sap. Thus the experiments are comparable 

 as regards the pectin content, but it is certain that the 

 amount of enzyme could not have been identical in the 

 different samples of sap, and the electrolytes also were 

 probably not quite constant in quantity. 



To standardize the apparatus, the time required for pure 

 water to flow out of the bulb between the two marks was 

 measured. For purposes of comparison one instrument 

 was chosen, and the slightly different times of flow for the 

 others were made the basis of factors by which the times 

 of flow of the pectin solutions could be recalculated for the 

 standard viscosimeter. As the absolute amounts of en- 



