460 ANDREWS: PROTOPLASMIC STREAMING IN Mucor 
figure that a three-way stopcock is inserted between F and G and 
also one between the U-tubes F’ and G’. This arrangement 
makes it possible to attach a tube at LZ or L’, and without dis- 
connecting or disturbing the apparatus to quickly draw off samples 
of the gas at these points and to ascertain if the chemicals in the 
various U-tubes are removing any objectionable substance from 
the gas and letting it pass through pure. The tests showed the 
hydrogen to be absolutely pure in the samples taken in this way. 
The tubes G and H and the bottle J contain pure water and 
pieces of wet filter paper to moisten the gas. Unless this is done 
the air which enters the gas chamber U’ will soon cause the drops 
of water, or other medium in which the plants are growing, to 
evaporate. 
The U-tubes G and H and the bottle J with the water they 
contain also act as a check valve to prevent a backward flow of any 
gas used. I used the bottle J instead of a third U-tube, so that a 
curved tube, 7, might be inserted in it with a narrow opening of 
known size to assist in estimating the rapidity of flow of the gas. 
It will be seen that C’, D’, E’, and F’ contain the same sub- 
stances as C, D, E, and F, but experience has shown that it is the 
better plan to use two sets, and that it avoids a possible early 
deterioration of any of the chemicals which might occur before the 
experiments were completed, if only one set were used. The 
U-tubes G’, H’, and J’ contain concentrated glycerin, and the arms 
of the tubes are loosely filled with pieces of filter paper saturated 
with the same solution to dry the air or gas drawn through these 
tubes. 
From either of the two rows of U-tubes above mentioned the 
gas may be drawn through O’ in two ways. It may 8° either 
through Z to the gas chamber U’, containing the plants under 
investigation, or through the stopcock P, then through R to the 
gas chamber U’. 
By the first way only gas of the temperature 0 
passed through U’. But by passing the gas through 
R it may be warmed to any temperature in R by wa 
water in R’ as desired before sending it to the gas chamber. 
; ; lied by 
more convenient way is to have the gas lamp X contro 
an accurate thermoregulator, or a still better method is to place 
f the room is 
P and then 
A 
