Ilex Aquifolium, L., in Reference to Specific Conductivity. 529 
fifteen times as long as broad, with {heir end-walls lying obliquely in the 
radial plane, inclined at an angle of about 30° to the longitudinal axis. 
The lateral walls show bordered pits when they are in contact with living 
cells and are strengthened by reticulate thickenings. The end -walls, which 
appear like bulging continuations of the lateral walls, are pierced by scalari- 
form perforations, separated by scalariform bars which may number 17 
or 18. The segments are in open continuity by means of the perfora- 
tions, and thus form true vessels. Their length cannot be determined 
accurately by longitudinal section, since they run through several centi- 
metres ; nor by maceration, as the segments separate very easily ; but 
reliable data can be obtained by injection with fine Indian ink. The shoots 
are soaked in water and the air removed by means of a suction pump : they 
are cut off (under water) as close to the base as possible and their basal 
ends immersed in a vessel of Indian ink : this is connected with a mercury 
pressure tube, which on elevation above the shoot will give a pressure of an 
atmosphere. The Indian ink is thus forced through the stem, the pressure 
being continued for 24 hours. When the shoot is removed, it is sectioned 
from the apex downwards, at intervals of 1 cm. The greatest height 
from the base at which the Indian ink is found in the wood indicates the 
length of the longest vessel. This maximum figure is indicative of the 
vessel-length, since the vessels injected do not show a continuous core of 
Indian ink, but a series of short interrupted columns, and many of those 
which appear to be empty in the basal region* are found to be injected in 
the higher levels. The vessel-length shows considerable diversity in 
different shoots, as can be seen from the following table : 
Distance of Section 
Number of Vessels 
from base in cm. 
injected. 
Shoot 1 
11 
5 
„ 2 
11 
5 
}> 3 
6 
3 
„ 4 
9 
3 
„ 5 
16 
3 
„ 6 
12 
3 
Thus the lowest figure (6 cm.) and the highest (16 cm.) represent 
lengths of stem in different shoots in which the vessels are continuous. 
These long vessels with their short segments and small scalariform 
perforations form the characteristic tissue of the wood, and no unperforated 
tracheides are found associated with them in the wood cylinder. But these 
latter elements are numerous at the periphery of the wood in the neighbour- 
hood of the insertion of the. petioles : they are of varying form, often short, 
wide, and irregular, and serve to connect the petiolar wood strands with the 
long vessels of the wood cylinder. 
The two-sidedness of the shoot, which is evident in the growth of the 
leaves, also shows itself in the anatomy. The cylinder of wood is widest on 
the abaxial and narrowest on the adaxial side of the stem. On the abaxial 
N n 
