The viscid pulp soon hardens, affording a protection to the seed; in germination the sucker-root penetrates the bark, and a connexion is established with the vascular tissue of the first plant.
c eun~7 Such an arrangement of vascular tissue is called radial, ~
The vascular tissue is typically separable into distinct collateral bundles (figs.
When the vascular tissue of such plants is arranged Camblum in separate bundles these are said to be closed.
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.