1911] SHULL—OXYGEN MINIMUM AND GERMINATION 459 
permitting me to see and compare my materials with the genus 
collection of Xanthiwm in the Field Museum of Natural History. 
a In determining the minimum oxygen pressure required for the 
initiation of protoplasmic activity, reduction of total atmosphere 
was employed. The apparatus used at first was a slightly modified 
form of that used by SCHAIBLE (25) in his experiments on the germ- 
ination and growth of various plants at reduced atmospheric 
pressures. In order to control the light, the germinators were at 
t MoM. 
Fic. 1.—Diagram of apparatus: a, capillary tube; b, wash bottle; c, two germina- 
tors with wet cotton, for lowers and uppers; ¢, pressure gauge; ¢, vacuum chamber 
e low pressure when the germinators are started, f, aspirator run 
by constant level system with a fall of 45 feet. 
first surrounded by opaque black paper; but later, when tempera- 
ture was found to be a very important factor in the result, and while 
testing the influence of temperature on the oxygen minimum, light 
and temperature were both controlled by placing the germinators 
in a water bath provided with a sensitive electric thermostat. A 
diagram of the apparatus is shown in fig. 1. 
The seeds were germinated on moist absorbent cotton, and a 
constant current of air was drawn into the apparatus through long 
Pieces of capillary tubing by means of powerful aspirators. In 
order to overcome the drying effects of a low atmosphere, a dish 
of water was set in each germinator in addition to the saturated 
