486 Priestley and Pearsall. — Growth Studies . III. 
tapering base of the container terminated in a three-way tap, the bore of 
the passages being 2 mm. 
Large seeds, such as beans, were used, and the germinated seed was 
wedged into the container neck, care being taken that the root was on the 
side of the neck opposite to the porcelain point, and the latter clearly visible. 
The container was filled with solution by allowing the latter to enter through 
the basal tap until it just touched the porcelain point. The volume of 
solution entering was measured, and this obviously would grow less as the 
roots increased in size — the decrease in 
volume of solution representing the 
increase in the volume of the roots. 
A number of containers could be 
used with the same refilling and 
measuring apparatus. % Generally six 
were employed, each containing a plant 
under observation. Except during a 
measurement, the containers were kept 
in a large water bath at a constant 
temperature of 15 0 C. ( + i°). The bath 
was covered over so that the roots were 
kept in the dark, the shoots being in 
the light. 
The containers were filled from a 
series of bulbs (RS, ST, &c., see figure) 
fed from a four-litre reservoir of nutrient 
solution. As the individual containers 
held various amounts from 3 1 5 to 358 c.c., 
the bulbs were arranged so as to run in 
any one of the four values 297, 310, 
322, and 335 c.c. with the minimum 
number of readings. With the arrangements figured, the discharge of 
any one of these volumes required only two readings of meniscus levels 
(at T or S and at R). The diameters of the tubes on which the level marks 
were made was about 5 mm., so that the readings involved only a small 
error at most. The point R was kept at a uniformly higher level than the 
top of the container. 
The containers could thus be nearly filled by running in a known 
volume from these bulbs. The final small amount of solution was added 
from a measuring tube, W Z, which consisted of two bulbs, and below them 
a long glass tube graduated in o*oi c.c. Any volume between o and 6 c.c. 01 
16 and 27 c.c. could be run in from this tube, and in conjunction with the 
various filling bulbs described it was thus possible to fill and measure 
the volume of solution in any container between 298 and 363 c.c. The 
Apparatus for measuring growth of roots in 
volume ; for explanation see text. 
