344 BOTANICAL GAZETTE [May 
MEASUREMENTS OF WIDTH OF CELLS OF CONCAVE SIDE—cont d. 
Apical Basal Average 
(4) 8 6 4 6 7 7 6 ws 6.71 
(5) 8 7 8 8 7 6 7. oa 7-42 
(6) 12 II II II II 12 13 ia L157 
(7) 15 5 15 15 15 12 13 a 14.28 
(8) 17 16 15 15 15 15 16 ae 15.57 
(9) 14 15 II Io II 12 10 “5 11.82 
(10) 15 15 15 is 15 II 16 a 14.57 
Average width of cells, - - - - 11.69 
The curvatures from which the above table was made are 
comparable to those described under tables I-IV. The angle 
of curvature is approximately the same, and growth for one hun- 
dred hours following the curvature has ensued. After the lapse 
of this period, the entire surface of the curved portion is free 
from root hairs. In addition to the disintegration of the walls 
of the root hairs, the external cells of the root have died. Inthe 
sections examined the epid l and two underlying layers of the 
concave side, and the epidermal and one layer on the convex side 
have collapsed. The total width of the section is 1.04™, of the 
cortical region of the concave side .342™™, of the convex side 
.24™™, and of the central cylinder .458"". The foldings of the 
end walls of the cells of the concave side have almost dis- 
appeared, and present a gently undulating outline, while those 
of the convex side are pronounced, exhibiting U or V outlines. 
In all of the curvatures of this stage of development initial lay- 
ers of secondary roots were to be found on the convex side of 
the cylinder only. In the above section the rudimentary root 
had pierced two or three layers of the cortical cells. This 's in 
accordance with the facts described by Noll, in which secondary 
roots were found to spring from the convex side of curving 
radicles only. While the initial cause of such an arrangement 
is not apparent, it is very easily seen that the formation of : 
branches on the concave side of the organ would not only entail 
the expenditure of many times as much energy in piercing the 
compressed cortex, but the tensile strength of the curved portion “ : 
