24 OBSERVATIONS ON FOSSIL VEGETABLES, 
so precisely with that of recent stems, that one can hardly hesitate to refer 
the one and the other to the same genus, although the differences exhibited 
by recent species of a genus are often so slight, that there appears little hope 
of our being able to distinguish fossil species by their internal structure, 
without including other characters. 
This much being premised, the remarks which I have to offer will an- 
swer better as referring directly to the Plates, than as forming the subject 
of a separate essay. 
EXPLANATION OF PLATE I. 
T's Plate contains representations of the internal structure of Recent 
Plants belonging to the Gymnospermous Phanerogamic, Monocotyledonous 
Phanerogamic, and Dicotyledonous Phanerogamic Classes. The portions 
represented are of very thin slices, viewed by transmitted light, and mag- 
nified about fifty-five times. 
Fig. 1. American Fir. 'Transverse section, shewing part of four of 
the concentric layers. 
Fig. 2. Indigenous Scotch Fir, from Invereauld, Pinus etna 
Transverse section, shewing a concentric layer, with part of two others. 
Fig. 3. Norway Fir. Transverse section, shewing a concentric layer, 
with part of two others. 
Fig. 4. Common Yew, Taxus bacctittt Transverse section, shewing 
part of four layers. 
Fig. 5. American Cedar, from Mobile. ‘Transverse section, shewing 
part of two layers. 
These portions of sections will be understood by making reference to 
Fig. 14, by which is represented part of a transverse section of a twig of Pi- 
nus balsamea, shewing, in the centre, the pith, composed of somewhat hexa- 
gonal cells, two entire woody layers, a portion of a third, the inner bark, 
the outer bark, and the epidermis. Figs. 1, 2, 3, 4, and 5, then, represent 
2 
