39 BOTANY. 
The foramen of the ovule is also called micropyle. The nucleus and 
integument are united at the base of the ovule by a cellulo-vascular 
membrane, called chalaza. The hilum indicates the organic base of the 
ovule, the foramen marking the apex. The primine, secundine, and nucleus, 
are always united together at some point of their surface. When this union 
takes place at the base of the ovule, as in its embryonic condition, this is said 
to be orthotropal, or atropal. When the ovule is curved downwards, so as 
to approach the placenta, it 1s camptotropal ; when curved downwards, and 
grown to the lower half, anatropal; when attached by the middle, so that 
the foramen is at one end, and the base at the other, it is campylotropal, or 
amphitropal ; when shaped like a horse-shoe, lycotropal ; when anatropal, 
with the raphe half loose, semianatropal. By raphe is meant the vascular 
connexion between the base of the ovule and the base of the nucleus, in 
cases where these two bases do not coincide as they do in the orthotropal 
ovules. 
An ovule is said to be ascending when attached to a parietal placenta, with 
the apex directed upwards. It may hang from an apicilar placenta at the 
summit of the ovary, and be inverted or pendulous ; or it may be suspended 
from a parietal placenta near the summit. When two ovules in the same 
cell are placed side by side, they are collateral, and their relative positions 
may otherwise vary. 
c. Fertilization. 
The fertilization of a flower usually results from the action cf pollen upon 
the stigma, which in some manner causes the development of an embryo 
within the nucleus. Authors disagree as to the precise manner in which this 
action is exerted. The theory most generally adopted is, that the pollen 
grains falling on the stigma are detained there, and soon exhibit a protrusion 
of the inner coat, or intine, in the shape of a tube, which penetrates the 
stigmas, and passes down through the style, ultimately to reach the embryo. 
The result of this action is the formation of a vital point (a single cell), which 
ultimately becomes the embryo, and from which a new plant may be produced 
by exposure to the proper conditions. Sometimes more than one embryo may 
be developed mm the same ovule. The embryo derives the material of its 
growth from the surrounding tissues, and the whole series of phenomena is 
attended by the evolution of heat, which sometimes is quite conspicuous. 
Authorities disagree as to whether or not the germinal vesicle exists in the 
embryo-sac before the application of the fovilla. In some cryptogamous 
plants the vital spores are discharged from their envelope without any 
apparent union of cells of two different sexual characters: in the Conferve 
and Diatomacez, however, there is a union of the contents of two different 
cells, by means of tubes, which are protruded from one into the other. This 
process, called conjugation, results in the production of germinating bodies. 
When the pollen of one species of plant fertilizes the ovule of another 
species, the result is a hybrid. These, however, are of rare occurrence in 
nature. 
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