OF MOVEMENT IN PLANTS. 73 
tendril fails to secure contact with a suitable object, it coils up freely, as already shown, 
and this is the necessary consequence of the normal changes in the tissues. If, however, 
it comes in contact with an object of support, the tendril coils about it and accomplishes 
its double spiral within the normal period of its growth. This period cannot be 
prolonged for the purpose of finding a suitable support or completing imperfect changes. 
These must all be accomplished before the wood and bast tissue—the latter in particular— 
reach a certain stage in the development of their permanent character. This is well 
shown in the fact that old tendrils, which have failed to grasp a support until very near 
the end of their activity, manifest a striking loss of sensitiveness, and often catch hold but 
imperfectly, or if they gain a firm hold, fail to perfect their double spiral. 
IJ.—Vitis CORDIFOLIA, Michz. 
In the tendril of Vitis, not only with reference to its sensitiveness and general cir- 
cumnutations, but more especially in its histological aspects, we have to deal with an 
organ which presents many features distinct from those of Cucurbita, the common ground 
of resemblance being found in functional similarity and in the way in which the circum- 
nutations arise. 
The tendril of the grape is a modified branch, bearing two smaller branches which 
serve a similar purpose. These branches, however, unlike those of the Cucurbita tendril, 
do not proceed from a common point of insertion, but arise successively on the elongating 
primary axis of the tendril as a whole. In their external aspects, they are well rounded, 
but somewhat flattened on the inner face toward the extremity, where the tip is strongly 
recurved. Throughout their length, the prevailing red color (V. cordifolia) is broken by 
ten narrow green lines, which are developed at approximately equal distances through 
the circumference. These are the bands of vibrogen corresponding to the three bands in 
the tendril of Cucurbita. Internally, the structure presents the features exhibited in 
Plate V. Figs. 1, 2, 3 and 4 a—during the earliest period of circumnutation—from which 
the following details may be gathered. The epidermis consists of a single row of thin 
walled cells with a strongly corrugated cuticle. Directly beneath this, lies a single row 
of pigment cells containing the red coloring matter. The hypodermal tissue consists 
chiefly of collenchyma, in which the angles are but slightly thickened (Fig. 3). As a 
whole, the tissue is quite continuous in most cases (Fig. 1, c/). Within the region of the 
hypoderma lie the ten vibrogen bundles, », v, v, etc., which are well defined from the 
surrounding tissue, but somewhat variable in size. These bands, although they fre- 
quently penetrate the collenchyma deeply, do not always break its continuity. Next 
within the collenchyma is a thin layer of very active fundamental tissue, the cells of 
which are large and regular (Fig. 1, pr). It is within this tissue that, at a somewhat 
later period, the cambium arises as a well defined layer. Directly internal to this is the 
wood zone, or xylem portion of the vascular bundles. This, in the earliest periods of 
circumnutation, is composed of somewhat isolated and nascent vascular bundles, the 
elements of which are all very thin walled and rapidly increasing (Fig. 44). The only 
structural element remaining is the pith, which, as in Cucurbita, bears no special relations 
to the circumnutations. 
Sec. IV., 1886. 10. 
