AN ENCYCLOPADIA 
we” ae 
OF HORTICULTURE. 539 
Ovule—continued. 2 
varies much; in some Ovules it is very long (see Fig. 
805), while others do not possess it. Most Ovules have 
it closely adherent to one side, the Ovule being in- 
A 
FIG. 804. ANATROPOUS OVULE OF ACTA SPICATA IN SECTION. 
Only one Coat exists on it. 
verted, or anatropous, as in Actea, so as to bring the 
micropyle close to the placenta, while the Ovule itself 
remains straight (see Fig. 804); other Ovules are curved 
Fig. 805. YOUNG CaMPYLOTROPOUS OVULE OF LYCHNIS DIURNA 
IN OPTICAL SECTION. The Funiculus is very long, and the 
Inner Coat projects considerably at the Micropyle. 
or campylotropous (see. Figs. 805 and 806), as in the 
Pea and in Lychnis; so that in them also the micropyle 
is brought near the placenta, but the funiculus is only 
Fig. 806. CAMPYLOTROPOUS OVULE IN SECTION, showing 
Two Coats. 
adherent slightly to one side of the Ovule. The form 
selected for description is called erect, or orthotropous 
(see Fig. 803). The Ovules of orchids have no fibro- 
vascular bundle in the funiculus. 
Development. This shows peculiarities in certain plants. 
In the Ovules of Santalum album, and occasionally in 
those of some orchids, there are two embryonal vesicles, 
so that two embryos may form in a seed. In seeds of 
Ovule—continued. 
Oranges, of the Spindle-tree, of Funkias, and of certain 
other plants, it is usual to find two, or even three or 
four, embryos. But this results from budding from the 
tissues of the nucellus of several small cellular growths, 
which push the wall of the embryo-sac before them, and 
occupy the place of the true embryo: the latter is 
usually crushed by them, and perishes. This process has 
been called Polyembryony. It is a case of vegetative 
replacing true sexual reproduction, and, by its discovery 
two or three years ago, various apparent anomalies in 
hybridisation have been explained. 
The processes of fertilisation, and of subsequent de- 
velopment, in the Conifers and other Gymnosperms, are 
so different in many respects from those above described, 
as to call for a brief notice. The Ovules are not in- 
closed in carpels, as in other flowering plants; but in 
general appearance and structure they do not show any 
marked peculiarities as contrasted with the Ovules of 
these plants. They are orthotropous in some (Yew), and 
anatropous in others (Pines, &.). They have only one 
coat. The contents of the embryo-sac, and the develop- 
ment of the embryo, are markedly different from what 
we find in other Phanerogams. At an early stage, the 
sac is filled with protoplasm, in which lies a single 
nucleus; but this very soon divides repeatedly (as in 
other Phanerogams to form the endosperm), and the sac 
may thus become more or less full of new cells, the 
temporary endosperm, ranged along the wall, or occupy- 
ing most of the cavity. Certain of these cells near the 
micropyle do not divide like the others, but remain 
larger than them. Each of these large cells after a 
time divides into a small cell above and a larger one 
below. The small cell may remain undivided, but usually 
divides into a rosette of four (¢.g., Juniper), or into more, 
arranged in two or three layers (e.g., Pines), forming the 
neck, or rosette cells. In each case, an opening is left 
between them down to the larger central cell. The whole 
body formed by the group of cells is known as the 
corpusculum. The number of corpuscula varies from 
three to fifteen. The pollen grain lies directly upon the 
micropyle, with no apparent effect, in most cases, for a 
long time; but at last it pushes a tube down to the 
embryo-sac, which is pierced, allowing the end of the 
tube to lie directly on the rosette cells, and to push 
between them into the upper end of the large central 
cell. Some of the substance passes into the latter cell, 
part becoming diffused, and part remaining visible for a 
time as an upper nucleus; but this nucleus afterwards 
becomes united with the true nucleus of the cell, to ae 
form a new nucleus. Then follows a series of cell- 
divisions at the lower end of the central cell, which 
result, in general, in the formation of four rows of 
side by side, lengthwise. The lowest cell of each row 
divides, to form an embryo. Thus, it is the rule for 
Gymnosperms to produce several embryos in a seed; but 
in most seeds only one embryo is fully developed, the 
others being destroyed by pressure of the one upon 
them. This one developed is nourished largely at the 
expense of the endosperm. 
Much use is made in Systematic Botany of the differ- 
ences in structure, form, and development of and in 
Ovules. 
The meaning of the lettering in the sections of Ovules 
is as follows: a, outer coat; b, inner coat; c, nucellus; 
d, embryo sac; e, micropyle ; f, stalk, or funiculus ; g, fibro- 
vascular bundle of stalks; h, chalaza; i, placenta, 
OXALIDEZ. A tribe of Geraniacee. 
OXALIS (from owys, acid; referring to the taste of 
the leaves). TRIBE Ozalidew of ORD. Geraniacee. 
A very large genus (upwards of 220 species) of green- 
house, hardy, or nearly hardy herbs, sometimes stem- 
less, with a bulbous or fleshy rhizome, sometimes 
