42 BOTANICAL GAZETTE | JANUARY 
sliced into the three strips as before. A considerable curve 
remained after the roots were freed from the bending force, and 
by measurement the convex side lengthened about 1™™, and the 
concave sideshortened about 1™. The shortening wasof course 
all due to forcible compression, and yet after separation of the 
tissues, the cortex on the concave side, both in water and in 10 
per cent. KNO, was somewhat longer than the axial cylinder. 
The cortex on the convex side was much longer than the con- 
cave cortex or the axial cylinder. This seems to make it rather 
improbable that the compression to which the concave side of 
the root may be subjected when it curves in response to a stimu- 
lus is sufficient to make the cortex shorter than the axial cylin- 
der. Consequently when the cortex of the concave side does 
become shorter than the axial cylinder, as was found to be the 
case in some of my experiments (table VII), it must be 
explained on other grounds than passive compression. That 
there is such a shortening of the cortex on the concave side in 
its relation to the axial cylinder is shown by experiments per- 
formed by Sachs (62) and Ciesielski (5), who found that when 
the root is split into halves and the half root is placed in a 
horizontal position with the cut face upward, the half root some- 
times remains straight, sometimes curves upward and some- 
times curves downward; whereas, if the half root is laid 
with the cut face turned downward, the curve is invariably 
downward. It has already been noted in this paper (page 
32) that when roots are split after they have begun to curve 
away from the brand on one side of the tip and the halves have 
been placed in an upright position, the curving of the concave 
half root toward the cut face is delayed, though it usually takes 
place later. The stimulus of burning one side of the root is a 
strong stimulus but applied for only a short time, and when the 
reaction from the effects of the stimulus sets in-there is no fur- 
ther stimulating effect. When roots are laid in a horizontal 
position, however, the stimulus is continuous and its effects 
therefore are cumulative so long as the root tips do not attain a 
vertical position. For this reason the stimulus of gravitation is 
