Section of Zoology and Botany, 497 



to the piece of wood in question ; whether it occurred in both the 

 stem and branches of Taxodium disticha ; whether it was peculiar 

 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. 



Third Series. Vol. 7. No. 42. Dec. 1835. 3 S 



