329 BOTANICAL GAZETTE [MAY 
constitute an important factor. . . . . Ifthe tip of a root is cut off square 
across, it does not exhibit traumatropic curvatures, but if cut obliquely it 
becomes curved, provided the cut is made to the right depth. t is 
plain that in order to induce traumatropic curvature with certainty by oblique 
cutting away of tissue at the apex, the cut must be made deep enough to 
affect the growing point itself. It is perfectly plain that the root cap may be 
cut deeply without curvature following. 
In my own work some experiments were made in an effort to 
bound the sensory zone. A root tip of Zea, branded in such manner 
that nearly all of the root cap was killed, as well as a sector of 
tissue beginning .5™™ back of the apex of the growing point and 
extending obliquely across, intersecting both sides of the cylin- 
der of periblem and including the entire apical part of the grow- 
ing point (fig. 7), exhibited marked curvature a few hours later. 
Fic. 2 
Fic. 1. Diagram showing extent of injury by branding, producing a curva- 
ture in a root of Zea. 
Fig. 2. Diagram showing extent of injury by branding, producing a curva- 
ture in a root of Pisum. 
In another instance, a root of Pisum, branded in such man- 
ner that the entire root tip and a sector .4™™ in length (axially) 
cutting both sides of the cylinder of periblem at an angle of 30°, 
produced a curvature ( fg. 2). A strong curvature was exhib- 
ited by a root of Phoenix from which a thin slice from the outer 
layer of the cortex back of the punctum vegetationis had been 
removed ( fig. 3). In like manner, a radial incision im the cor 
tex of a root of Arisaema at a distance of 1.5 from the tip gave 
a decided reaction (jig. 4)- These results suggest that the sen- 
sitive zone includes that portion of the periblem lying basal to 
the perpendicular — the axis of the root at the growing 
