1904 | BENNETT: ARE ROOTS AEROTROPIC 255 
diffusion of the gases, the gelatin was smeared over with olive 
oil and the surface opposite the roots melted off with a hot 
needle. Thus, just as far as possible, the cross-diffusion of gases 
was confined to the vicinity of the root-tips, and the tips were 
exposed to the gases, except for the very thin covering. Air 
and CO, were introduced on opposite sides of the seedlings, and 
eect i = a $i ait 
SE eet Lees ‘ — 
_— Sea <— eer Le 
[m= Mig inn. eS Cs - —e ee rs 
(ii. ene: a i ites he 
= ‘cinooth = ao case. =< Ry ~ 
a Oe Ste Siig ls ey Mi. — tei ee eee 
Fic. 5.—A, seedling; a and e, bars of wood; 4, wide strips of glass; ¢, narro 
Spaces; d, narrow strips of glass sealed on; 4, height of water; /, spaces filled with 
gelatin, 
at the close of 42 hours it was found that, while there had been 
very little growth, there had been no curves. 
Thinking to determine roughly the rapidity of diffusion of 
gases in such contrivances as have been described above, one 
block of gelatin, made alkaline and colored with phenophthalein, 
was opposed to one saturated with CO,, and the septum of 
gelatin in fig. 5 was made pale red and the CO, and air brought 
On opposite sides as in the experiment. In the former case, 
Within 4 hours the gelatin was decolorized to a depth of 10™™ 
and in 24 hours the entire block had lost the red color; while in 
the preparation shown in fig. 5 the gelatin was entirely decolor- 
ized in 134 hours. Judging from these two tests, the CO, must 
