12 Hydration and Growth. 



glass tubing with thin walls, drawn to a point and sealed in a flame. 

 The pointed glass tip fits into a hole in the center of a thin glass plate 

 resting on the sections to be swelled. The attachment of the swinging 

 lever to the free end of the bearing lever may be adjusted to give an 

 amplification of the swelling, which is recorded by the pen tracing an 

 inked line on a sheet of paper 8 cm. wide ruled to millimeters. The 

 paper is coiled inside a brass cylinder and issues through a slit passing 

 to the drum of a clock of the same pattern as used on standard thermo- 

 graphs in such manner as to present a uniform plane sin-face to the 

 action of the pen in all parts of its arc. The tautness of the paper may 

 be varied by altering the position of the slit in the brass cylinder and 

 clocks may be employed which give the paper a motion of 28 cm. in 

 24 or in 168 hours. The two levers are connected with a short length 

 of jeweler's chain to minimize friction, and the base of the frame carry- 

 ing the levers is seated on the top of a rack-and-pinion column with a 

 vertical motion of 12 cm. and is capable of being fastened rigidly at 

 any height within its range of 10 to 12 cm. (fig. 1). 



The dishes finally selected for containing the sections to be immersed 

 in solutions were of the Stender type, 5 cm. in diameter and 24 mm. 

 deep. It was foimd advisable to have the surface of the bottom inside 

 the dish ground plane in order to avoid slipping and movement of the 

 swollen sections and of the delicate jellies formed by the biocoUoids 

 when in states of extreme hydration. For similar reasons it was neces- 

 sary to place the entire preparation on a concrete pier, or still better 

 upon a slab of marble, granite, or concrete, "floated" in a large box 

 of sandy loam which had a direct bearing on the ground. The dishes 

 containing the sections were seated on various supports, the best form 

 being that of an iron or concrete cylinder about 12 cm. in height and 

 10 cm. in diameter. Three soft-metal studs were let into the basal 

 end of this cylinder to give it a three-point bearing on the marble slab. 

 With preparations made in this manner and with the counterpoise 

 arranged to give the least weight upon the swelling objects compatible 

 with a steady following movement of the pen, it was possible to obtain 

 valuable records of the velocity and course of swelling of sections of 

 plants and of various colloidal substances. It was soon learned that 

 more reliable results might be obtained with thin sections, in which 

 the coeflBcient of expansion would be high and complete hydration 

 would be attained quickly and with less dispersion of the colloid in 

 the liquid. 



No records of temperature in the earlier tests were kept, but any set 

 of swellings, generally of three or four different solutions, were carried 

 on simultaneously and under the same conditions. It is to be under- 

 stood, therefore, that in tabulated data, as table 2, the relative swell- 

 ing of sections of one sample in the different solutions at the same time 

 only may be compared. The experiments had not been carried very 



