1904 ] BENNETT; ARE ROOTS AEROTROPIC 243 
of Michigan during the years 1900-1902, under the supervision 
of Professor Frederick C. Newcombe, to whose valuable sugges- 
tions and constant assistance is largely due whatever of merit 
this paper may possess. It is with pleasure that I here acknowl- 
edge my indebtedness to him. 
II. EXPERIMENTAL INVESTIGATION. 
It has been my purpose to determine the following points as 
definitely as possible: whether roots are aerotropic under natural 
conditions ; and whether they are aerotropic under any conditions. 
Observations have been made of the effect of oxygen, hydrogen, 
carbon dioxid, and, as a test, illuminating gas, these being 
allowed to flow against one side of roots in gaseous form or dis- 
solved in gelatin blocks. This is the same as the effect of a less 
and a greater pressure of oxygen than the normal atmospheric 
pressure. 
I. With roots in water. 
In the series of experiments under this head, the seedlings 
were grown in filtered tap-water and placed parallel to one 
chamber, or between two chambers of gas, which usually had a 
parchment membrane closure. 
At the outset several methods of experimentation were em- 
ployed to determine whether roots of Zea Mays grow straight in 
water if supplied with a larger proportion of oxygen than usual. 
In one series, seedlings having roots from 10 to 15™ in length 
were secured to the sides of inverted air chambers, without mem- 
branes, immersed in the water, the kernels of corn being above 
water, and the root tips just below the lower edge of the chamber. 
The root tips were thus from 5 to 10™™ from the air in the im- 
mersed chamber, but g°™ or more from the air above the water 
in the larger chamber. Observations showed that of 20 seedlings 
used, 7 turned toward the air.in the immersed chamber, 4 away, 
3 in other directions, and 6 remained straight. 
In another series, seedlings supported, as in all the following 
experiments when necessary, between two strips of moist blotting 
paper held firmly to small pine rods by rubber bands between the 
Seedlings, were suspended over a chamber which was connected 
