Botanical Collectioiis. 311 



enable us to distinguish the one tribe from the other. In the coniferae 

 there is only one regular system of pores, resembling a piece of the most 

 delicate network. Each mesh is bounded by straight lines crossing each 

 other at nearly right angles, and the concentric lines of the meshes almost 

 always approximate each other at the outer edge of each annual layer of the 

 wood. This structure is iniiform throughout the whole tribe of coniferae, 

 the only perceptible difference consisting of the dimensions of the meshes, 

 trees of slow growth, as Taxus Baccata, having the finest texture. It may 

 be right to mention, that in some of the coniferae, (not in all,) there are 

 occasionally circular openings to be seen, known to botanists under the 

 name of Lacunte. These, however, are very irregular in their distribution, 

 sometimes occurring frequently, at other times not at all. 



The structure of the true dicotyledons consists of a system of vessels, 

 separated from one another by masses of cellular matter. The vessels, ox 

 pores are always bounded by curve lines. In some trees they are circular, 

 in others they are elliptical, and the degree of eccentricity of the ellipses in 

 different trees is remarkably different. The elliptical pores are sometimes 

 divided by one or two transverse partitions. In some trees the vessels are 

 empty, and in other trees they are filled with a resinous or gummy-resinous 

 matter. The size, form, number, and arrangement of the vessels, or pores 

 differ so widely in different trees, that one species may be as clearly distin- 

 guished from another by the organic structure, as by the shape of the leaves 

 or the florification. As in the coniferae, the vessels generally become 

 smaller as they approach the outer edge of the annual layers. In some 

 kinds of trees the vessels are numerous, in other kinds they are sparingly 

 bestowed ; and it is worthy of note, that, in some kinds of wood of great 

 strength and durability, as the oak, they are not only numerous, but also of 

 very large dimensions. 



The cells constituting the cellular portion of dicotyledonous trees, have 

 different forms and different dimensions in different kinds of wood. In 

 the coarser kinds of mahogany, for instance, the cells have a rhomboidal 

 form. In some trees they are spherical, and in others the form is very 

 irregular ; but however the form may differ, it will in general be found that 

 the smaller the cells, the greater will be the strength of the timber. This is 

 very strikingly the case with regard to the different kinds of elm. In the 

 Scotch elm, the cells are smaller than in the English elm, and these, again, 

 are smaller than in the Dutch elm ; and it is generally known the timber of 

 the Scotch elm is better than that of the English, and that the Dutch elm 

 is good for nothing Ibid. 



Euphorbia retusa. — Two apparently different species are confounded under 

 this name. The one is E. retusa, Cav. ; this has the seeds white, prisma^ 

 tical, and marked with six deep longitudinal grooves ; the glands of the 

 involucre are red ; the leaves obcordate. The other is E. retusa, D. C. ; 

 this has the seeds of a gray colour, four angled, tuberculated, or almost 

 transversely wrinkled ; the lower leaves retuse ; the glands of the involucre 

 are also red as in the other. The plant of D. C. agrees in almost every 

 point with E. exigua, and is surely only a variety ; that of Cavanilles appears 

 to be distinct : both grow about Montpellier. Eu. rubra, Cav. (not D. C.) 

 is perhaps identical with E. terracina, and scarcely differing from E. proving 

 cialis ; it has little relation to E. retusa, with which it is often confounded. 

 (W-A.) 



Flora Virgiliana " Having been requested by some literary friends to 



furnish the botanical names for the plants mentioned in Virgil, particularly 

 in the Eclogues and Georgics, I send you the following. I ought to observe, 

 that it is a subject of considerable difficulty, as the allusions to the plants by 

 the poets are generally very vague ; and, indeed, some of the species are 



