34° BOTANICAL GAZETTE [ MAY 
direction, and the radial walls are folded more sharply than 
those of the layers near the epidermis, or in the same region in 
younger curvatures. The difference in the 
. granular densities of the cortical regions of 
nae Sa the convex and concave sides has nearly 
disappeared. However, the membranes of 
the entire concave side have become much 
heavier. The epidermal cells of the con- 
vex side, as well as the underlying two or 
three layers, have evidently undergone pas- 
sive stretching. The longitudinal walls have 
been brought closer together, and in some 
instances the appearance of collapse is pres- 
ent. The end walls of the epidermal cells 
are distorted obliquely, but on account of 
their greater thickness do not exhibit the 
sharp foldings of the subepidermal layers. 
The inner layers of the cortical region have 
rounded turgid outlines, and the curves of 
the walls are wavy in outline, indicating that 
these cells have been most active in produc- 
ing the elongation of this side of the organ. 
Intercellular spaces are larger and more 
Fic. 6. Longitud- abundant than in the concave side. 
inal sections through = The apical portion of the root, 1.2™" in 
curved portions of root length, has become quite straight, and the tip 
beret nti no longer exhibits traces of the strain exerted 
excitation. C, convex UPON it by the curving forces when the motion 
‘side. A, concave side began. The forward limit of the region of 
_ (see tables V-VI). —s curvature is quite sharply marked (jig: 6). ae 
TABLE VIL. 
Median longitudinal section of Zea mais, placed vertically upright and 
curved through 160°. The measurements were made in that portion of the 
root in which the first geotropic excitation occurred, and this part of the Cor 
vature was seventy hours old, and exhibits an angle of 90°. 
