540 Rivet t . — -The Anatomy of Rhododendron politician, L., and of 
is succeeded by a descent below the leafy nodes, but this gives place to 
another ascent before the rapid fall to the apex. The first steep rise 
indicates a great increase in the number of vessels in the first elongated 
internodes (see Curve E) : these supplant the fibres which act as supporting 
tissue, at the extreme base. They form the vascular tissue which supplies 
the young transitional leaves which unfold rapidly in the first warm spring 
weather. The subsequent descent in the curve is due to the decrease in 
average size of the vessels (see Curve D), and also in some cases to a slight 
falling off in the general increase in number. The second rise in the curve 
is due sometimes to a slight increase in the size of the vessels at the 
beginning of the foliar region and to the general increase in number, but as 
the large vessels are mostly at the inner margin of the wood and are laid 
down before the leaves expand, this cannot be correlated with the activities 
of the leaves. The final fall of the curve is due to the rapid decrease in 
the size of the vessels as the apex of the stem is reached. The irregularities 
of the curves in individual shoots are seen to be considerable, but they 
appear to be chance variations in the differentiation of permanent tissue, 
rather than a response to the mechanical and transpiring necessities of the 
leaves. These irregularities make it evident that a considerable latitude 
in specific conductivity is to be expected, and this agrees with the experi- 
mental results obtained by Professor Farmer, which are detailed below. 
The levels of the curves are very Similar in the shoots of Group A and 
Group B, and this agrees with the similarity of the figures for specific 
conductivity. These latter lie between 11*2 and 13-9, while the means of 
the percentage figures in the segments of the shoots selected for experimental 
purposes lie between 20 and 22. This correlation can be traced throughout 
by reference to the following table : 
Mean Figures for the 
Shoot. 
Experimental 
Sp. Conductivity. 
percentage of IVood 
occupied by Cavities 
in the Experimental 
Segments. 
C 1 
16.4 
24*0 
C 2 
15.0 
23-6 
C 3 
16.9 
24*0 
D 1 
18.6 
25.8 
D 2 
18-2 
25*5 
D 3 
20-8 
26.5 
E 2 
21.8 
27.9 
18.6 
25.8 
e 4 
20-7 
27-2 
e 5 
19.4 
26-0 
E 6 
15-5 
23.6 
In the holly shoots the C curves show a general rise from the base to 
a maximum somewhere near the apex of either the two-year-old or one- 
year-old segments, and then fall away to the terminal bud, but, as in Curve B, 
the general trend is obscured by sudden interruptions at the yearly joints. 
The position of the maximum indicates that the first- and second-year wood 
