258 BOTANICAL GAZETTE [APRIL 
To verify this conclusion, a preparation was made in which 
the roots were placed between two cork plates set in the same 
damp-chamber, with the same evaporating surface as before. 
Six pea seedlings were set up in the ordinary manner, the 
roots being 2 to 3™" from each cork plate. After 2 hours, I root 
was touching one plate of cork; after 3 hours, 4 were touching 
this plate; and at the end of 24 hours, 2 roots were touching 
one cork, 2 the other, I was straight, and 1 had grown out 
beyond the two plates. 
The evidence was absolutely convincing that here were purely 
hydrotropic curves. The cork surfaces had acted as evaporating 
surfaces in a chamber of the kind ordinarily said to be saturated 
with moisture. Accordingly it is highly probable that Molisch’s 
damp-chamber, which had relatively less evaporating surface 
than mine, was not saturated with moisture and that the curves 
he obtained were hydrotropic rather than aerotropic. 
III. DEDUCTIONS FROM EXPERIMENTS. 
In my experiments, roots of Zea Mays, Pisum sativum, Rapha- 
nus sativus, Cucurbita Pepo, and Lupinus albus have been subjected 
to the one-sided access of oxygen, hydrogen, and carbon dioxid, 
to determine whether these roots do really curve toward or 
away from these gases in natural or artificial conditions. 
Incidentally I have offered my solution for the curvatures of 
roots recorded by Molisch and by him termed aerotropic. 
_ 1. When the roots of the various seedlings mentioned in this 
paper were grown in water between submerged chambers, the one 
containing air and the other CO, or H, no constant and regular 
curvatures were observed. Under these conditions the majority 
of the roots were indifferent to the influence of any of these 
gases. The same results followed when the roots were not sub- 
merged in water, but placed between the gas chambers in a 
larger damp-chamber. 
2. When the seedlings were grown in a thin, vertical layer of 
earth, forming a septum between air and CO,, or air and hydro- 
gen, or in earth permeated on one side with air and on the other 
with CO, or hydrogen, very few curves were formed, the large 
