178 
ORGAI^OGRAPHY. 
BOOK I. 
necessarily originate in the margins of the earpellary leaf : and 
hence they have been compared to the buds found upon the 
margins of some true leaves, and may be shown to be actually 
analogous to them in structure. 
Of the truth of this there can now be little doubt; for, to 
say nothing of such plants as Bryophyllum, which habitually 
form buds on the margins of the leaves, or of Malaxis 
paludosa, in which the edge of the leaf is frosted by little 
miscroscopical points, that are neither exactly ovules nor 
exactly buds, or of the bracts of Marcgraavia, which Tur- 
pin, with much ingenuity, has endeavoured by mere argu- 
mentation to prove analogous to the primine of the 
ovule, it h^s been shown by Henslow that in the Mignio- 
nette the ovules do actually become transformed into leaves, 
either solitary or rolled together round an axis, of which the 
nucleus is the termination. (Cambr. Phil. Trans, vol. v. 
part i.) Engelman also mentions and figures instances of 
similar changes ; but he does not say in what plants, nor are 
his figures by any means satisfactory. He, however, concludes 
from the observations of himself and Schimper, that " the 
ovules are buds of a higher order, their integuments leaves, and 
their stalk the axis, all which in cases of retrograde metamor- 
phosis are converted into stem and green leaves." {De An- 
tholysi prodromus, § 44. 76. t. 5. 4, 5.) I should rather say 
that the evidence goes to prove that the ovule is a leaf -bud in 
a particular state, that the integuments are scales (z. e. rudi- 
mentary leaves) rolled up and united at their touching mar- 
gins, and that the nucleus is the growing point, to which I 
have already on so many different occasions directed attention. 
In almost all cases the ovule is enclosed within an ovary, 
as would necessarily happen in consequence of the convolute 
nature of the earpellary leaves : but if the convolution is im- 
perfect, as in Reseda, the ovules are partially naked; and if 
it does not exist at all, as in Cycadeae and Coniferae, the 
ovules are then entirely naked, and, instead of being fertilised 
by matter conveyed through the stigma and the style, as 
in other plants, are exposed to the direct influence of the 
pollen. This was first noticed by Brown; and, although since 
contradicted, seems to be perfectly true. 
