208 
ORGANOGRAPHY. 
BOOK I. 
the shell of the ovary, or by the separation of the mass of 
ovules into distinct parcels upon the placenta. 
It seems to me difficult to explain the usual nature of the 
pistil and its parts more simply or in a more satisfactory 
manner than this ; but Schleiden altogether objects to that part 
which attributes the placenta to the developement of ovules 
upon the edge of a carpel, or from a carpel at all. He 
maintains that the formation of the ovule in Taxus, — where 
it terminates a branch, and is naked, and where the leaves are 
arranged in the customary spii’al direction, even to the ex- 
treme summit, and where no one leaf implies in the slightest 
degree an adaptation to the female part more than another, — 
is incompatible with this theory ; and he also adverts to the 
difficulty of explaining by it such a structure as that of 
Armeria, in which five carpels surround a single ovule, rising 
from the bottom of a cell upon a cord, which curves down- 
wards at its apex, and thus suspends the ovule free in the 
centre of the cavity; he therefore supposes the ovule, and 
consequently the placenta, to be in all cases a production of 
the axis. As the opinions of Dr. Schleiden are in my mind 
always deserving of great attention, I extract a rather long 
passage from his paper on this subject. 
“ Although we cannot doubt that in plants possessing a 
free central placenta, or in those where, as in the Polygonaceae, 
Taxus, Juglans, Myrica, the placenta cannot be supposed to 
exist as a separate organ, the nucleus of the ovule is only the 
summit of the axis, yet the question suggests itself as to how 
the parietal placenta is to be understood ; and I do not con- 
sider the explanation to be very difficult. We find in many 
Arace® that the axis is expanded at its summit into a kind 
of disc, upon which is a number of buds or ovules, arranged 
like the flowers in the capitulum of Compositae and other 
families. We next observe these discs expanded into lobed 
processes, and adherent to the edges of the carpellary leaves 
in all parietal or pseudocentral placenta ; such a modification 
of the axis as this is what occurs in Dorstenia. The parietal 
placenta may be explained equally well, and perhaps with 
greater simplicity, as a mere ramification of the axis. It will 
