460 DR. P. GROOM AND MR. W. RUSHTON ON THE STRUCTURE 
Thus from the diameters of the spring-tracheids in these last three forms 
we can form по conclusion as to the amount of water required by them in 
the substratum, though analogies with the American species indicate a 
considerable rainfall. On the other hand, they suggest a means of obtaining 
collateral evidence as to the climate under which fossil pines grew. 
From the structure of the leaves of P. longifolia and P. Merkusii we should 
conclude that stomatie transpiration can be vigorous, as stomata are present 
on the outer (lower) face as well as the flanks. 
(c) Shapes of Ordinary Tracheids. 
The tracheids running longitudinally in the wood belong to two main 
: g, 
(ii.) much shorter, “septate” or parenchymatous tracheids, whose terminal 
walls are transverse. The latter, which especially occur iu the vicinity of 
the resin-ducts, will be described in connexion with these. 
The majority of ordinary tracheids, whether they be the relatively thin- 
walled well-pitted spring-tracheids, or the thick-walled fibro-tracheids of the 
summer-wood, are straight and have more or less tapering, sharp or rounded 
ends. When abutting on a medullary ray the end may fork, or bend so as 
to run for some distance along the ray and thus form a transition towards a 
ray-tracheid, or may bend even through an angle of 180°, or finally may end 
squarely and abruptly against a ray-tracheid. These ends of the tracheids 
may bear pits in contact with the ray-tracheid, therefore on the terminal, or, 
types: (i.) ordinary long, more or less prosenchymatous tracheids ; and 
M! a v 3 
in a sense, tangential walls. 
But Pinus Khasya and P. Merkusit, also show bundles of tracheids which, 
though not connected with medullary rays, yet are bent towards their ends, 
the curvature being mainly in a radial plane, so that in extreme cases these 
are seen cut transversely in longitudinal, especially tangential, sections. On 
the bent parts of these tracheids bordered pits are abundant on the tangential 
walls and even on the blunt terminations. As these bundles frequently 
form a radial sheet only one tracheid in thickness, in transverse section they 
are denoted by a radial series of tracheids with tangential bordered pits in 
the spring-wood or summer-wood. 
(d) Arrangements of Bordered Pits on the Radial Walls. 
The bordered pits are oval or circular in surface view in the spring-wood, 
where they are ranged in one row, with occasional pairs, in P. excelsa and 
P. Gerardiana, in one or two rows in P. longifolia and P. Khasya, and in 
one, two, or three rows or in peculiar nests, of 3 or 4 in P., Merkusit (P1.25. 
figs. 47, 48). The species that has triseriate pits is also the one that shows 
the greatest radial width of tracheid. But an examination of the statistics 
