MEANING OF THE TERMS ENDOGENOUS AND EXOGENOUS. 221 
On the Meaning of the Terms Endogenous and Exogenous, 
as used by Botanical Writers.— In the language of botany, and 
especially by those writers who treat of the natural system, the above 
terms are in frequent use, as designating the different manner of 
growth exhibited in the two grand classes, Monocotyledonece and 
Dicotyledone<% —that is, plants which rise with one or two seedleaves, 
or cotyledons. To beginners in the study of the science, or even to 
those who are readers only, every term should be explained; and, 
therefore, it is only necessary to observe that the terms are compounds 
of two Greek words, viz. Endogenece, from endon, inside, and geinomai , 
to grow—that is, growth proceeding from within; and Exogenece , from 
exo, outside, and geinomai , to grow—that is, growth upon the exterior: 
consequently all plants which are increased by the addition of new 
members from within, are called Endogenous; and those which are 
enlarged by additions on the outside, are designated Exogenous. 
Modifications of the same terms have been used by some vegetable 
physiologists, to express the passage of fluids through the membranous 
partitions of plants. If a fluid issue from within, it is said to be 
exosmose ; but if inducted, it is called endosmose. 
Familiar examples of each character will be the best way of explain¬ 
ing them ; and, therefore, it is only necessary to select two well-known 
plants belonging to each—say, for instance, the common oak, and the 
equally well-known tulip. 
That the diametric bulk of the stem or trunk of an oak-tree is annu¬ 
ally enlarged by new layers of bark and wood on the outside is per¬ 
fectly evident. The heart or centre of the axis of wood is first formed, 
and the layers of the circumference last; the term exogenous is, there¬ 
fore, properly applied in speaking of the manner of accretion of that 
tree. 
All other trees and shrubs which rise from their seed, and are 
enlarged like the oak, belong to Exogenece. This manner of growth is 
necessary to the well-being of the plants themselves; because, if an 
exogenous plant receive any external injury, the wound is soon closed 
again by the new growths of bark and wood. The same constitutional 
property of the vitality being seated on the exterior, is of the greatest 
importance to the cultivator, because it is this circumstance which 
renders all our operations of budding, grafting, layering, and raising 
young plants from cuttings practicable, which could not be accom¬ 
plished were the vitality seated in the interior of the system. The 
living membranes of the graft and stock being placed in contact with 
each other, form the desired union; and in the processes of layering, 
