90 
PLANT MORPHOLOGY. 
quite complicated, as in the pea. The number of fibro- 
vascular bundles is more or less dependent upon the 
number of carpels that make up the gynoecium; as a 
rule, there is a strong fibrovascular bundle which cor- 
responds to the midvein of each carpel. 
The placenta is a development from the inner epi- 
dermis, and is traversed by a fibrovascular bundle 
from which branches are given off to the individual 
ovules; it may have a conducting tissue similar to 
that found in the style, and in some cases the epi- 
dermis of the stalk of the ovule may be developed to 
a stigma-epithel. 
The ovule not only possesses a distinct form as 
already given, but the internal structure, by reason of 
the changes associated with fertilization, is more or less 
characteristic for certain species and genera. It has 
an epidermal layer, the outer walls of which are more 
or less cutinized, and it consists for the most part of 
parenchyma cells rich in organized cell-contents and 
food-materials; and in addition the embryo sac contains 
a number of nuclei. The stalk and raphe are con- 
nected with the placenta by means of a fibrovascular 
bundle. 
The nectar may be secreted by the epidermal cells of 
various parts of the flower; these may resemble the 
ordinary epidermal cells or they may be modified to 
papillae, as in the spurred stamens of the violets, or to 
hair-like processes, as in Malva. The cells which 
secrete nectar constitute the “ nectar-apparatus,” and 
the walls are usually thin and more or less cutinized. 
The nectar-apparatus is found more generally upon 
some part of the stamen, while the calyx and corolla 
are not infrequently hollow or spurred at the base, 
which adapts them for holding the nectar, as in Lirio- 
dendron, Tropxolum, and the violets. 
