262 Holmes. — Observations on the Anatomy of 
The vessels formed in the beginning of the second annual ring in A 8 are 
much wider than any present in the first ring, as is usual. 
Curve B shows the total area of all the vessel cavities in each section, 
and represents the absolute water-conductivity. It is obtained by combin- 
ing the data from curves F and E, and shows in general a corresponding 
decline from the base to the apex of the shoot. It is to be noticed that 
both the curves A and B reach a lower point in the terminal internode of 
A 6, in which the apical bud is weak, than in that of A 4, in which the bud 
is stronger. The higher figures for A3, internode 11, are to be connected 
with the presence of two pairs of leaves above this point, instead of one 
pair as in A4 and A 6 ; see Fig. 3. The same applies in the case of A8#, 
internode 6, as seen in Fig. 1. The values for curves A and B in the smaller 
shoots A 8 b and A 8 e are very much lower. 
The specific conductivity for water is represented for comparative 
purposes by the percentage of the area of the wood occupied by the 
cavities of the vessels which it contains, in transverse section. This is 
shown in curve C. It depends upon the number of vessels present in a unit 
area of the wood as given in curve D, as well as upon their average width 
as discussed above for curve E. The figures for curve C are obtained most 
easily by combining the data from curves A and B. 
Curve D gives the number of vessels per square millimetre of wood for 
each section. The numbers vary between 32 and 633 in the four larger 
shoots, with a higher range in the others. It will be seen that the curve 
rises from the base upwards for each shoot, indicating that the wood is 
richer in vessels near the apex, and richer in fibres near the base, where 
mechanical support is necessary. The ascent of the curve is especially 
rapid near the apex, because of the smaller size of the vessels in this part as 
well as their close packing. In this connexion the high values for curve D 
in A 8 b and A 8 e are due both to the much smaller proportion of mechanical 
elements in these weak shoots, and to the small diameter of the vessels. 
Curve C serves as a measure of the specific water-conductivity of the 
wood, as explained above, in so far as it can be determined in transverse 
section. In general, the curve rises and then falls, the maximum occurring 
nearer the apex of the shoot than the base. In other words, up to a certain 
point the increase in the number of vessels, ,per unit area, makes the wood 
more efficient for water-conduction, its merely strengthening function being 
gradually reduced, but when the vessels get very small, the wood becomes 
less efficient again, their walls occupying a relatively larger area in propor- 
tion to their cavities. The rise and fall are shown in a general way by 
a comparison as a whole of the three curves for A 8 ; the figures are low for 
A 8 where there is a fairly high proportion of fibres, and fairly low again 
for A 8 e, where the vessels are very narrow. The sharp drop in curve C for 
the final internode in A 8 b is interesting in view of the failure on the part 
