88 
ORGANOGRAPHY. 
BOOK I. 
essentially distinct organs ; but, since the appearance of an 
admirable treatise by Goethe in 1790, On the Metamorphoses 
of Plants^ proofs of their being merely modifications of one 
common type, the leaf, have been gradually discovered ; so that 
that which, forty years ago, was considered as the romance of 
a poet, is now universally acknowledged to be an indisputable 
truth. It may, however, be remarked, that when those who 
first seized upon the important but neglected facts out of 
which this theory has been constructed, asserted that all ap- 
pendages of the axis of a plant are metamorphosed leaves, 
more certainly was stated than the evidence would justify ; 
for we cannot say that an organ is a metamorphosed leaf, when, 
in point of fact, it has never been a leaf. What was meant, and 
that which is supported by the most conclusive evidence, is, 
that every appendage of the axis is originally constructed of the 
same elements, arranged upon a common plan, and varying in 
their manner of developement, not on account of any original 
difference in structure, but on account of especial, local, and 
predisposing causes : of this the leaf is taken as the type, 
because it is the organ which is most usually the result of the 
developement of those elements, — is that to which the other 
organs generally revert, when, from any accidental disturbing 
cause, they do not sustain the appearance to which they were 
originally predisposed, — and moreover, is that in which we 
have the most complete state of organization. 
It is not my intention to enter into much separate discussion 
of this doctrine ; proof of it will be more conveniently ad- 
duced as the different modifications of the appendages of the 
axis come separately under consideration. The leaf, as the 
first that is formed, the most perfect of them all, and that 
which is most constantly present, is properly considered the 
type from which all the others are deviations, and is that 
with the structure of which it is first necessary to become 
acquainted. 
