252 BOTANICAL GAZETTE [APRIL 
wide by 1™ thick, inclosed in an iron wire gauze cage which was 
fitted in as a partition so closely between the sides of a glass jar 
that gases brought into the two chambers thus formed could pass 
over only through the earth or sawdust. This chamber was care- 
fully covered; the seedlings were kept constantly moist; and the 
CO,, or mixture of CO, and air, on one side, and air on the 
other, were forced in from a gasometer or water stream air-pump 
at the same rate and equally moist. By such a method there 
was certain to be an access to different gases on opposite sides 
of the roots. 
Regardless of the percentages of CO, used, the results were 
not indicative of aerotropism; 14 roots bent toward the earth 
through which air was flowing, 14 away, and 28 grew in the 
vertical plane. Pisum sativum, Lupinus albus, and Zea Mays ( pop- 
corn) were used in this experiment. 
From these two methods of experimentation it is seen that, 
while 221 representative seedlings were exposed to the one-sided 
application of a normal pressure of oxygen as opposed to some 
mixture of gases having a less pressure of oxygen or none at all, 
and while they were otherwise in almost natural conditions, still 
only 45 turned toward the source of oxygen, while 48 turned 
away, and 128 remained neutral.’ Certainly no one would con- 
tend that such results indicate that the roots are aerotropic, 
though they do show some disturbance in the direction of growth. 
4. With roots in gelatin. 
In the use of gelatin a medium was found that would permit 
of growth of the root, while preventing a rapid diffusion of gases. 
Solutions of 6 or 7 per cent. of gelatin in distilled water were 
thoroughly saturated, when cold but before solidifying, with air, 
hydrogen, or CO,, either by forcing the gas through the solution, 
or with the solution in an air-tight chamber by exhausting and 
refilling the chamber with the gas which passed through the 
gelatin as it entered. These solutions were allowed to harden 
for twelve hours, standing in chambers of air, or hydrogen, oF 
CO,, as the case might be, in paper-lined, rectangular dishes, 
20™ by 12™ by 4°, into which they had been poured when 
