54 PENHALLOW ON MECHANISM 
At the three points a, a’, a”, the continuity of the collenchyma is interrupted by 
groups of parenchyma tissue, which extend as longitudinal bands throughout the entire 
length of the arm. This tissue has certain important distinguishing characteristics. The 
cells are usually large, well rounded, and thin walled (Fig. 1, aa’, and Fig. 5). They-contain. 
an abundance of protoplasm and chlorophyll, and possess all the features of cells in an 
active condition of growth. Indeed, the activity of this tissue is conspicuous from the 
earliest period of circumnutation until long after the surrounding parts have become 
hard and woody, and all motion has ceased. Within the area of this tissue are to be 
found intercellular spaces (not shown, however, in the figure) together with their corres- 
ponding stomata, which latter are confined to the epidermis of these bands. The very 
large amount of chlorophyll here present, is the means of that outward distinction to 
which we have already referred. Inwardly, each of these groups of cells connects directly 
with the pith region of the tendril, thus causing a further break in the continuity of the 
interior tissues. From the very prominent part which this tissue evidently takes in the 
circumnutations of the tendril, and the frequency with which pointed reference must be 
made to it, we have deemed a descriptive term essential. We have, therefore, applied to 
it the name of “ Vibrogen” or “ Vibrogenic tissue,” as signifying that the origin of the 
ordinary cireumnutation is to be found there. 
Immediately internal to the collenchyma is a zone of rather large, thin-walled paren- 
chyma tissue, c, usually disposed in three or four rows, of which the innermost cells are 
the smallest. This tissue, which is essentially the mesophleum of the stem, forms a 
continuous zone through each of the vibrogen bands. The cells are filled with proto- 
plasm, and contain some granular, matter and a small amount of chlorophyll, which 
imparts the subdued green color to the tendril as a whole. The tissue presents all the 
characteristics of active growth, but it in all probability is inferior in this respect to the 
energy of the vibrogen bands—as will appear later—though it undoubtedly contributes 
its part as a factor in the general circumnutation. Directly interior to this tissue is the 
bast zone of the liber. At a very early period in the growth of the tendril, the bast 
portions of the vascular bundles establish conjunctive growth, and thereby form a zone (d), 
the continuity of which is interrupted only at those three regions where the vibrogen 
establishes its connection with the pith. In its earlier period of growth, the bast cells 
are all thin walled (Fig. 2 4). They are then in a condition of active growth, and are 
capable of conforming to the general and rapid elongation of the organ as a whole. It is 
this condition which essentially characterizes these cells during the greater portion of the 
tendril’s active period, but most conspicuously so during the earlier portions of it, since 
we find that, with the growth of the organ, the bast cells gradually increase in thickness 
and assume more and more completely their true character as permanent structure. And 
this becomes more conspicuous towards the end of the active period, when the motion of 
the tendril is gradually retarded, and becomes continually more spasmodic, until finally 
it ceases altogether. We then find that from thin-walled cells the bast has changed to 
thick-walled, permanent tissue, as shown in Fig. 28. This, then, defines the hard and 
woody character of the tendril, which is so conspicuous a feature after coiling. 
It is important to point out in this connection that as soon as this woody character 
in the tendril is fully developed, all motion must cease; and since the lignification is a 
gradual process, and will be completed within a definite period—assuming constant 
eel 
