66 SOME RECENT RESEARCHES IN PLANT PHYSIOLOGY 



The recent work of Haynes (1914) on the action of salts 

 of the alkalies and alkaline earths upon pectin will be con- 

 sidered farther on. 



THE ACTION OF PECTASE. 



Since there is no chemical method at all suitable for 

 following the course of the gelatinization of pectin by 

 pectase, recourse was had, at the suggestion of the author, 

 to the measurement of the viscosity of a mixture of enzyme 

 and substrate at regular intervals of time and at various 

 temperatures. It is at once evident that the chemical 

 change is not -proportional to the alteration in viscosity. 

 In spite of this the method enables one to obtain much 

 information as to the character of the reaction and the 

 factors which influence it, as will be seen from a study of 

 the viscosity time curves given by Ball. 



PREPARATION OF PECTIN. 



As a source of pectin, Ball employed the roots of the 

 carrot, Daucus carota. These were finely minced and 

 heated for two hours on a water-bath. Sufficient water 

 was added to cover the material. The pulp was then 

 pressed, and a little oxalic acid added to precipitate cal- 

 cium ions. After filtering the pectin was brought down 

 by mixing an equal volume of spirit with the extract. This 

 was collected on a filter and redissolved in a small quantity 

 of hot water. Further addition of alcohol caused the 

 pectin to be precipitated in its usual mucilaginous form, 

 and its removal from the liquid was effected by means of 

 a centrifuge. In this manner it was obtained in a fairly 

 pure state, and was then dried on a water -bath. On ad- 

 dition of hot water it readily redissolved, and was made 

 up to a 2 per cent, solution for use with the viscosimeter. 

 A few drops of toluene were added as a preservative. 



