4 3 2 Spalding. — On the Traumatropic 
curved, provided the cut is made to the right depth, as appears 
from the following experiments : — 
1 2. The radicles of six specimens of Vicia Faha were cut 
as indicated in Fig. 7, two along the line a a, removing a small 
portion of the growing-point, two along the line d a, so that 
a small portion of the root-cap alone was removed, and two 
along a line midway between these, approaching very closely 
the growing-point, but lying in the tissue of the root-cap. 
When next examined (time not stated in laboratory notes, 
but within twenty-four hours), the first two were found to be 
strongly deflected — 'bent up like a hook’ — while the remaining 
four were either straight or so slightly curved as not to 
suggest the effect of cutting. 
13. The experiment was repeated with four specimens of 
the same species, the radicle of one being cut along the line 
a a, those of the three others to different depths along lines 
parallel to a a , but with care not to cut deeper than the root- 
cap. Seventeen hours later the one deeply cut was strongly 
curved away ; the rest showed no change of direction. Similar 
experiments, which it is unnecessary to record at length, were 
repeated with like results. 
It 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 certain that the root-cap may be 
cut deeply without curvature following. 
Location of Sensitive Tissue. 
The preceding experiments lead to the inference that the 
tissue lying just beneath the root-cap is sensitive, and receives 
a stimulus to which, after induction, the root responds by 
bending. To test this farther, and to locate more definitely, 
if possible, the sensitive tissue, the following experiments were 
performed : — 
1 4. Ten specimens of Vicia Fab a with vigorous radicles 
from 1 to 2 cm. long were selected and their root-caps 
removed with a sharp razor. The operation is a delicate one, 
