468 BOTANICAL GAZETTE [ DECEMBER 
Respirometer.—This piece of apparatus (jig. 2) is a modifica- 
tion of one employed by Pfeffer, which in turn was adapted 
from Pettenkofer’s apparatus for experiments upon the respira- 
tion of animals. It consists of a small chamber in which germi- 
nating seeds or other living material is placed, surrounded by 
water to keep the temperature uniform. A thermometer is 
plunged in the chamber, and one in the water outside. 
Two U-tubes containing potash, and a wash bottle containing 
barium hydrate solution, are connected in series with the cham- 
ber at one end and withan aspirator, or water pump, at the other. 
At the beginning of an experiment the aspirator draws the air 
out from the chamber through a direct connection, and forces it 
through the potash tubes and wash bottle back into the chamber, 
freeing it of carbon dioxide in the operation. When the cham- 
ber is sufficiently free of carbon dioxide, the direct connection 
with the aspirator is broken, and a stopcock opened which pet- 
mits the carbon dioxide free air, forced into it by the aspirator, 
to pass into and traverse a long tube (about a meter) partly filled 
with a solution of barium hydrate (made by adding 15® of 
barium chloride to 5! of distilled water, and after it has largely 
dissolved adding 105* of barium hydrate), the gas then passing 
through a short supplementary tube, also containing barium 
solution. The bulbs at the distal ends of these tubes are to pre- 
vent an overflow, if a sudden increase in pressure should occur. 
There are two sets of tubes so that continucus observations may 
be carried on as long as desired. When the test has been 
progress for the first period (usually an hour), a three-way cock 
‘Unters. a. d. bot. Inst. zu Tiibingen 1: 637. 
Fic. 2. Respirometer. 
