26 Tans ley and Chick . — Notes on the 
very narrow hydroids, square in section, each abutting on four 
or usually five living cells (cf. Bastit, Fig. 2, PL XIII). 
In longitudinal section the middle row of living cells is 
clearly seen to consist of leptoids, many though not all of the 
cells having the characteristic bulging ends and very thin 
transverse walls (Bastit, PL XIII, Fig. 4 in P . juniperinuin). 
Though many of the facts relating to the passage of the 
leaf-traces through the cortex have been described by Haber- 
landt (pp. 404-5) and Bastit, we have thought it well to 
describe the histological features fully, as their accounts are 
by no means complete, and a full understanding of the 
relations are necessary to an appreciation of the morphological 
nature of the different tissues of the conducting system. 
On entering the cortex the leaf-bundle at first maintains 
its general form, though the characteristic shape of the leptoids 
in longitudinal section does not appear to be maintained 
during their passage through the cortex, and the inner layer 
of accompanying starchy cells frequently becomes somewhat 
irregular. 
The outer and inner rows of starchy parenchyma have dark 
brown walls, while the light yellow walls of the leptoids stand 
out clearly against the thick dark brown walls of the outer 
cortex. 
No marked change of form is noticeable on the transverse 
section till the Vllth trace (Fig. 20) counting inwards is 
reached. This trace has arrived at the somewhat smaller- 
celled and thinner-walled abundantly starchy layer forming 
the extreme internal layer of the cortex, which we propose 
to call a rudimentary pericycle (see above, rud. per., Fig. 20). 
As the inner layer of living cells of the trace reaches this, 
its cells change their character, becoming larger and lighter 
walled, in fact assuming the characters of the pericycle itself. 
At the same time the whole trace lessens its tangential length, 
becoming isodiametric instead of band-shaped, increasing the 
number of its leptoids from a single band of about six to 
nine or ten in a group, while the hydroids begin to lose their 
regular arrangement (Fig. 20, VIII and IX). The trace now 
