120 
M. J. Lynn 
Exp. 2. All the seedlings showed normal upward curvature 
when left in ordinary air and light—as in the first experiment 
tabulated. 
Exp. 3. All seedlings showed normal curvature when taken out 
of jar and left in air and light. 
Exp. 5. Seedlings showed normal geotropic curvature after having 
been left in air and light for a day. 
Exp. 12. These seedlings were photographed in the jar, when 
showing reversed curvature (see Plate I, fig. 1). The carbon dioxide 
was removed from the jar on the afternoon of Nov. 22nd and the 
seedlings left in air and light. On the following morning all the 
seedlings showed a normal upward curvature. They were again photo¬ 
graphed (see Plate I, fig. 2). The hypocotyl of the 7th seedling was 
too short to show curvature. 
Exp. 15. Nine of these seedlings showed a very definite curvature 
downwards at first, but after some hours two of the seedlings showed 
a negatively geotropic curve. The seedlings were photographed while 
still in the jar. An examination of Plate I, fig. 3 will show the two 
seedlings referred to above, and it is clear from the photograph that 
the first curvature was in a downward direction. The box of seedlings 
was taken out of the jar and after twelve hours in air and light the 
hypocotyls of all the seedlings showed a normal negatively geotropic 
curvature (see Plate I, fig. 4). 
Exp. 20. These seedlings had been brought on in bright light, 
hence because of active photosynthesis the carbon dioxide of respira¬ 
tion had not accumulated to any extent before the seedlings were 
put into the jar. This fact would probably account for the normal 
curvature, because a higher percentage of carbon dioxide would be 
necessary to decrease alkalinity sufficiently to produce reversed 
curvature (see below). 
Exp. 22. After four hours in the atmosphere containing 8-2 per 
cent, carbon dioxide, two of these seedlings showed a slight upward 
curvature and the remaining five were still quite horizontal. On the 
following morning all the seedlings had a normal upward curva¬ 
ture. Again in this case the seedlings had been brought on in bright 
light. 
Exp. 23. The downward curvature was slight in these seedlings, 
and was not apparent until several hours had elapsed. 
