308 BOTANICAL GAZETTE [may 
cave side of these organs, and that the elements of the tissue 
are arranged with comparatively large intercellular spaces in a 
manner which allows of great and sudden variation in the water 
contained in the active cells. The action of such tendrils is 
therefore generally similar to that of pulvini. I have pointed 
out, moreover, that the features of curvature of the tendrils 
examined do not agree with those of the stems, and that all ten- 
drils do not produce curvatures inthe same manner. Attention 
has been called to the fact that pulvinar mechanisms may be 
held to be characteristic of organs in which rapid movement of 
great amplitude is desirable, and that slower and more general 
movements, where great tension is essential, are brought about 
by elongation of the convex sides of the motor organs (14). 
In the course of the work upon tendrils, it was found neces- 
sary to make some comparisons of the action of certain dorsi- 
ventral members of this class with that of young roots of radial 
structure in the formation of reaction curvatures. The facts 
concerning the behavior of roots were not described or referred 
to, and during 1895 and 1896 work upon these organs has been 
carried steadily forward. 
In a general comparison of the conditions prevalent in curv- . 
ing roots and tendrils, it is to be seen that while certain general 
mechanical similarities are present, yet the actual conditions are 
widely different. The fibro-vascular tissue is in the form of a _ 
central cylinder (more or less incomplete) in the tendril, while 
in the root it is either in the form of a rod or cylinder, but is not 
fully formed in the motor zone of the root, while tendrils do not 
acquire the power of reaction until the central cylinder is well 
differentiated. Furthermore, tendrils are furnished with a sub- 
epidermal layer of collenchyma tissue, sometimes two oF three 
cells in thickness; a mechanical equivalent is wholly lacking 
from most roots. The greatest interest centers in the cortex am 
its relations to the water conducting or receiving spaces and ves- 
sels, since the force which gives rise directly to curvature arises 
_or is released in the cortical parenchyma. In Passiflora the com 
tex of the tendril is supplied with a great abundance of intercellu-_ 
