MO eee shes a ats geet en EN Repe eV A ye eee ee Me i ee 
1897 ] THE CURVATURE OF ROOTS 359 
underneath the epidermal layers. The epidermal system exhibits 
similar reactions to those of Zea, except that the changes are 
relatively greater than in Zea, due no doubt to the greater thick- 
ness of the root and the consequent greater distance of the 
epidermis from the central cylinder. The arms of the lever 
extending from the periphery of the concave to the convex side 
would be twice as long as thatof Zea. The above differences 
are mechanical, but the cortex of Phoenix also offers distinct 
differences in behavior from that of Zea. The axial diameter of 
the cells of the concave side has not increased, and is not greater 
than that of the same region apical to the curvature. The 
increase of the radial diameter has been very slight. The cells 
of the cortex of the convex side have increased in radial as well 
as axial diameter, ina manner similar to that in stems as described 
by Kohl (12), and by Noll (17). It is difficult to account 
for the similarity of the behavior of the curvatures of roots of 
Phoenix and dicotyledonous stems, except as a concomitant of 
the mechanical structure, though the real necessities are not 
apparent. 
Differences inthe quality of the membranes are not so easily 
distinguished in young roots asin old stems. The sections of 
the roots of Zea which have been excited geotropically for three 
hours and stained in Bismarck brown exhibit slight differences 
between the cortex of the convex and concave sides. Those of 
the concave side have taken the stain more deeply and are thicker 
than those of the convex side. After remaining forty-eight 
hours in alcohol the membranes of the convex side appear only 
slightly tinted and are not so highly refractive as those of the 
concave side, which are still more deeply colored. These results 
do not bear strict comparison with the reactions of stems, since 
the action of the agents used in killing and imbedding might 
cause some alterations in the physical properties. From the 
Steat amount of data given in the foregoing tables it is possible 
_ to obtain some evidence bearing upon the question. The follow- 
ing table presents the general results obtained from the meas- 
urements of Zea. 
