CHAP. I. 
REGULAR METAMORPHOSIS. 
531 
principles that govern the structure of one individual, will 
also be true of all other individuals. 
It is particularly requisite that this should be clearly under- 
stood, in order that a just estimate may be formed of the 
nature of the proofs to be now adduced in regard to the 
doctrines of morphology. Whatever can be demonstrated to 
be true, with regard to one single individual, is true of all 
other individuals : whatever is proved with reference to one 
organ, is proved by implication, as to the same organ, in all 
other individuals whatsoever. 
Moreover, the fact of one organ being readily transformed 
into another organ, is in itself a strong presumption of the 
identity of their origin and nature ; for it does not happen 
that one part assumes the appearance and functions of another 
if they are essentially different. Thus, while the functions of 
the hand may be performed by the feet, as we know they oc- 
casionally are in animals, nothing whatsoever leads the heart 
to perform the functions or assume the appearance of the 
liver, or the liver of any other organ. This is one of the 
arguments of Linnaeus. 
The first organ which requires consideration is the stipule. 
It is not present in all plants ; but, when it does exist, is 
found at the base of the footstalk of the leaves. It generally 
is a membranous process, with a bundle of vessels passing up 
its centre ; or it is entirely destitute of a vascular system. In 
the rose the former is the case ; but nothing is more common 
than to find a leaflet accompanying the stipule ; and in a 
specimen of Rosa bracteata which I once had in my posses- 
sion there were no stipules, but, in their stead, two pinnated 
exstipulate leaves. Hence stipules are to be considered as 
rudimentary leaves. 
The bracts are the organs intermediate between the leaves 
and the calyx. Their nature is extremely various ; some- 
times they have a greater resemblance to the leaves, and 
sometimes to the calyx. In some roses, as R. canina, they 
are obviously dilated petioles, to which a leaflet now and then 
is attached: in other species, as R. spinosissima, they differ 
in no respect from the other leaves. In the tulip a bract is 
occasionally present upon the scape, a little below the flower ; 
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