As a result of this extension of the umbrellar margin, all structures belonging to this region, namely, the ring-canal, the nerve-rings, and the rim of thickened ectoderm, do not run an even course, but are thrown into festoons, caught up under the insertion of each tentacle in such a way that the ring-canal and its accompaniments form in each notch of the umbrellar margin an inverted V, the apex of which corresponds to the insertion of the tentacle; in some cases the limbs of the V may run for some distance parallel to one another, and may be fused into one, giving a figure better compared to an inverted Y.
in height until the lower parts are well thickened, when it may be allowed to acquire the allotted height by moderate annual increments.
This consists of elongated cells with cellulose walls, which are locall~ thickened along the original corners of the cells, reducing the lumer to a cylinder, so that a number of vertical pillars of cellulose con nected by comparatively thin walls form the framework of th~ tissue.
Thus the structure of an old thickened root approximates to that of an old thickened stem, and so far as the vascular tissue is concerned can often only be distinguished from the latter by the position and orientation of the primary xylems. The cambium of the primary root, together with the tissues which it forms, is always directly continuous with that of the primary stem, just in the same way as the tissues of the primary stele.
Isolated celh (idioblasts), thickened in various ways, are not uncommonly founc supporting the tissues of the leaf.