548 Rivelt . — The Anatomy of Rhododendron ponticum , Z., and of 
below. The rise at the base corresponds with the rise in Curve C, showing 
that the first increase in vascular tissue is due to an increase in number. 
The steep rise at the apex is not shared by Curve C, showing that here 
the increased number of vessels will not make up for their small lumina 
from the point of view of water-conduction. The figures calculated vary 
from 556 at the base of Shoot E 5 to 1,908 at the apex. 
In holly the most marked characteristic of the E curves is the sudden 
fall at each yearly joint. The fall is due, as already indicated, to the large 
number of fibres developed in those internodes between the winter-bud 
scales. In reality, though they occupy several nodes, their influence in the 
length of the stem is very slight, because at these regions the nodes are 
much crowded together. The figures calculated vary from 330 to 755 in 
Shoot F and from 439 to 1,238 in Shoot K, so that we have among all the 
shoots a minimum of 330 and a maximum of 1,238 vessels per sq. mm. 
The individual variations in the form of the curves are not sufficient to 
warrant a separate description. 
Comparison of Results. The general points of resemblance between 
the corresponding curves which have been figured for Rhododendron ponticum 
and holly have already been noted. They are also shared by the curves 
which have been figured elsewhere for the stool shoots of hazel and ash. 
It must be remembered, however, that whereas it is only the one-year-old 
wood which has been analysed for rhododendron, ash, and hazel, the 
observations extend through shoots of four or five years for holly. Thus, 
in comparing the curves, only the apical segments in Shoots H, K, L, and 
M of holly should be referred to. 
The irregularities of the wood area curves (A) (most marked in 
rhododendron) have no great significance arid do not warrant further 
description. 
The C curves show considerable divergence in the four woods 
examined. In rhododendron and holly they rise steeply from the base 
of the one-year-old segments. The maximum in holly is reached more 
or less in the middle, but generally nearer the apex than the base. The 
maximum in rhododendron may be reached either nearer the base or 
nearer the apex : in several cases the maximum is reached nearer the apex 
on account of the increase in size of the vessels in the leafy part of the 
stem. The holly is a comparatively small-leaved plant, and the vessels in 
the stem which link on to those in the petiole are much smaller than the 
normal found at other levels, while in rhododendron this is not so. Also 
in the holly the separation of each year’s growth into a leafless and leafy 
region is not nearly so marked as it is in rhododendron ; the transitional 
leaves are comparatively few in number, and permanent foliage leaves may 
be found at the lower nodes ; thus the anatomy in holly shows less 
variations in analysis than does the rhododendron. 
