No. 379.] REVIEWS OF RECENT LITERATURE. 531 
and the results are tabulated in measurements of various parts of 
these organs. 
Dr. Ewart finds that in a purely physiological sense a series of 
connecting forms exists between the simpler forms of climbing hooks 
as seen in Uncaria and the highly specialized tendrils of the Passiflora 
type. The simplest type of all is represented by the hooks in Ces- 
alpinia, Rubus fruticosa, etc., where their use in climbing is purely 
accidental, in consequence of which fact they do not thicken on con- 
tact. Next in the series comes Luvunga, possessing non-irritable 
spines and irritable climbing hooks, followed by the type represented 
by Uncaria and Artrabotrys, where only the irritable clasping hooks 
are found. In his work only the last two were experimented with. 
Next in order come forms like Roncheria and Ancistrocladus, where, 
besides the thickening, the sensitive region shows a slightly increased 
curvature produced by contact alone. Finally, in forms represented 
by the root tendrils of Vanilla, tendrils of Cucurbita, Passiflora, 
Sicyos, etc., is presented the phenomenon of rapid and, at first, 
transient curvature by contact alone. In such cases it is the alter- 
ation in the turgidity of the parts that effects the change. 
Dr. Ewart goes on to say that no hard and fast line can be drawn 
between a mere contact and a pressure stimulus. Irritable hooks are 
adapted to respond to pressure more readily than do tendrils, the 
latter being affected to a greater degree by contact. In certain cases 
at least, pressure and traction stimulate cambial activity correspond- 
ing to the mechanical requirements of such cases. Contact stimuli 
appear to affect only the outer layer of cells directly, the curvature 
resulting being due to the transmission of an impulse. The weak 
stimulus afforded by injury to the parts concerned is probably to be 
explained by the normal increase of activity, a kind of tissue pyrexia, 
which is known to follow wounding. 
In cases where the curvature is slowly produced, as in Strychnos, 
the change cannot be due to any alteration of turgidity but to an 
heterauxesis in the cambial growth. 
Irritable hooks and tendrils, regarded in analogy with other irri- 
table organs, are parts which respond as a whole when any portion 
of them is stimulated, the result varying, of course, with the point of 
application and the nature of the exciting stimulus. In conclusion, 
the author says that the irritation caused by contact stimulus, in the 
Strict sense, is limited almost wholly to the concave surfaces of 
the hooks. When the pressure is increased to bring about an inter- 
nal mechanical strain, a response is eventually to be noticed, but 
