Ilex Aquifolhim , Z., in Reference to Specific Conditctivity . 533 
outermost zone of wood contains elements not altogether differentiated. 
In all the conducting elements bordered pits can be seen in transverse 
section wherever they are in contact with living cells or with other water- 
conducting elements. 
The fibres, in transverse section, are much smaller than the water- 
conducting elements, and have thick walls staining deeply with safranin. 
They show slightly bordered pits, where they are in contact with living 
cells, but not where they abut on water-conducting elements. The living 
cells are largest in the multiseriate medullary rays : they have thick walls, 
protoplasmic contents, and a small quantity of starch. 
In longitudinal section the water-conducting elements of the primary 
xylem are found to be long narrow vessels with spiral and annular thicken- 
ings, which do not separate into segments on macerating, but appear as long 
tubes without obvious remains of cross-walls. They are mostly under 
a centimetre in length. The conducting elements of the secondary xylem 
are elongated segments, about thirty to forty times as long as they are 
broad. The end-walls lie in an obliquely radial plane and are pierced by 
narrow, scalarif <?rm perforations, separated by numerous narrow bars. Thus 
they form continuous vessels, which separate into segments on macerating, 
but on injection appear as tubes which rarely reach 3J cm. in length. No 
segments with unperforated cross-walls were observed, except in the 
junction tissue between the wood cylinder and the petiolar strands, where 
numerous irregular tracheides are to be found. The bordered pits are 
abundant wherever the vessels are in contact with living cells : they are 
frequently accompanied, especially in the outer zones of old stems, by spiral 
and reticulate thickenings. 
Method . The general method employed for the analysis of the wood 
is that put forward by Miss Holmes 1 in her paper on hazel-wood. The 
internodes of each shoot were numbered from base to apex and transverse 
sections made in the midst of certain internodes. The sections were stained 
with haematoxylin and safranin and first examined under a very low power 
of the microscope (2-inch objective). The limits of the wood were traced 
on paper by means of a camera lucida at a magnification of 21 diameters. 
By means of a planimeter the true area of the wood was determined and 
calculated in square millimetres. Subsequently the wood was examined 
under a high power of the microscope (one-sixth inch objective), and again, 
by means of a camera lucida, an exact representation of the cavities of the 
water-conducting elements in a sector of known area was drawn on milli- 
metre-squared paper. From this drawing the total area of all the cavities 
was obtained by counting the square millimetres which they contained. 
The number of elements in the known sector was also counted. Thus the 
1 M. G. Holmes : A Study in the Anatomy of Hazel-Wood with Reference to Conductivity of 
Water. Ann. Bot., vol. xxxii, 1918. 
