EXPLANATION or tHE WOOD-CUTS, 
ILLUSTRATIVE OF THE 
NATURAL AND ARTIFICIAL DIVISIONS. 
FLowE RING Plants are grouped naturally into two great Classes, 
the Dicotyledones or Exogenz, and the Monocotyledones or Endo- 
gene, (which terms are often anglicised into Dicotyledons or Exogens, 
and Monocotyledons or Endogens;) and after a little practice, almost 
every species may be very readily referred to its proper Class, with- 
out the necessity of recurring to any of those minute but most impor- 
tant characters by which it is primarily distinguished. Notwithstanding 
the great dissimilarity which subsists between such prominent organs 
as the stems, leaves, and flowers of plants in the same class, we may 
almost always detect some peculiarity or other in the structure of each 
of them, which alone is sufficient to indicate the class to which the 
plant belongs. There are certainly a few anomalous cases which will 
sometimes puzzle even the experienced botanist, but generally speak- 
ing it requires very little practice to enable any) one to proneaies ata 
single glance, to which of these two cl flowering pl 
a 
The first cuts, figures 1 and 2, by which we illustrate one of 
the important distinctions between these two great classes, re- (2H 
fer to the internal organization of the stems, more especially 
in such as are woody. One class has been termed “ Exogene,” 
(zw exo, outside, yevvaw cennao, to beget) because the stems of axe 
the woody species are increased by an annual deposition of new 
wood on the outside of that which was previously formed. At first they 
“consist only of a central column of pith, composed of cellular tissue, 
(which is made up entirely of little membranous bladders, forming in- 
numerable cells) and surrounded by a cylinder of vascular tissue (which 
consists of delicate tubes or vessels) and this cylinder is termed the 
medullary sheath; and this again is ee by a ome —— skin 
or epidermis. Fresli tissue, ( Is,) i Il} 
developed between the inedallary sheath and epidetnis; one ie part of 
which, in contact with the former, becomes a zone of wood, and the 
2 
