The arrangement of the conducting tissue in the stem is characteristic; a transverse section of the very young stem shows a nunber of distinct conducting strands - vascular bundles - arranged in a ring round the pith; these soon become united to form a closed ring of bast and wood, separated by a layer of formative tissue (cambium).
A, The main anatomical features of a cycad stern a Spermatozoids may be summarized as follows: the centre is from G of fi occupied by a large parenchymatous pith traversed g; by numerous secretory canals, and in some genera c p onen-grain by cauline vascular bundles (e.g.
In addition to these cauline (fi rstcell).(After strands (confined to the stem and not connected Webber.) with the leaves), collateral bundles are often met with in the pith, which form the vascular supply of terminal flowers borne at intervals on the apex of the stem.
The pith is encircled by a cylinder of secondary wood, consisting of single or multiple radial rows of tracheids separated by broad medullary rays composed of large parenchymatous cells; the tracheids bear numerous bordered FIG.
Secretory sacs occur abundantly in the leaflamina, where they appear as short lines between the veins; they are abundant also in the cortex and pith of the shoot, in the fleshy integument of the ovule, and elsewhere.