74 
BRITISH ASSOCIATION.- 1835. 
to that kind of wood; or whether it was a general feature in the ho¬ 
rizontal branches of other Coniferce. 
The first step in the investigation was to procure another branch 
of Taxodium disticha. This he did last summer, and marked the 
upper side before the branch was cut off. The structure of this 
branch agreed in every respect with that of the branch formerly ex¬ 
amined, and the pale-coloured or narrowest side was the uppermost. 
The next step was to ascertain whether the stem of Taxodium di¬ 
sticha agreed in structure with the branches. For this purpose the 
author requested Mr. James Macnab, of the botanic garden of Edin¬ 
burgh, to bring him from America a portion of a stem. This he 
was so kind as to do last winter. The stem was five inches and 
three tenths thick in the longest diameter. The pith was nearer one 
side than the other by three quarters of an inch. The surface of 
the cross section was of a uniform pale colour, with the exception 
of a spot surrounding the pith nearly an inch in diameter, of a 
slightly darker shade. On examining a number of sections of this 
stem, they were all found to agree with coniferous stems in general, 
and showed not a trace of the structure occurring in the under side of 
the horizontal branches. 
Having thus ascertained that in Taxodium disticha the differ¬ 
ence of structure alluded to was peculiar to the horizontal or nearly 
horizontal branches, the third step was to determine whether any 
other coniferous horizontal branches agreed in structure with 
those of Taxodium disticha . With this view Mr. Nicholas lately 
procured branches of ten different species of Pines, and has found 
them all agreeing in structure with those of Taxodium disticha. The 
pith is always nearer the upper than the under side. The upper or 
pale portions have discs similar to those of the stems, and show no 
trace of decussating fibres in the vessels or spaces containing the 
discs. The under or darker-coloured portions have fewer, smaller, 
and more obscure discs than those contained in the upper part, and 
the spaces between the vertical partitions in both the longitudinal 
sections have decussating fibres, which, however, are often finer and 
more crowded than those in Taxodium disticha. 
It may be right to remark, that in coniferous horizontal branches 
the pith is always more or less eccentric, and that in some instances 
the eccentricity is great. In a branch, for example, of the black 
spruce, the cross section, which is somewhat ovate, has a vertical 
diameter of three inches and three tenths. The distance of the pith 
from the upper side is only half an inch, and from the under side it 
is two inches and eight tenths. There are thirty distinct annual layers 
in the under side; but these thirty layers, when crowded into the space 
of half an inch in the upper side, are so minute that they can scarcely 
be enumerated. This, however, is an extreme case, the pith being 
in general less distant from the centre. The branches of some pines, 
particularly the larch, are nearly cylindrical, but even in these the 
pith is always out of the centre. 
But although the upper and under sides of many, perhaps all, co¬ 
niferous branches, present a different structure, yet such a difference 
