THE FLOWER ~ 83 
nucellus divide, giving rise to a regular tissue, which almost 
fills the ovule. Atthe apex of this tissue, or endosperm, one 
or more ege-cells, or oospheres, are seen. All this takes some 
months and precedes fertilisation, which does not occur till 
the year after pollination. Fertilisation is the union of a 
portion of the pollen grain with the oosphere; the result 
of fertilisation is that the oosphere is converted into an 
oospore, from which the embryo arises. The embryo will be 
found developed in the second year’s cones, the large green 
succulent ones; whilst a third year’s cone will contain the 
ripe seeds, which will show the following parts: 
1. A testa developed from the single integument of the 
ovule ; 
2. The endosperm enclosing the embryo ; 
3. The embryo consisting of radicle, plumule, and cotyledons. 
From the embryo the root and shoot arise. — 
In comparing the flowers of Angiosperms with those of 
Gymnosperms, the essential difference to note is this: In 
Gymnosperms the macrosporophylls are flat and open, so that 
the ovules (macrosporangia) are exposed ; whilst in Angio- 
sperms the macrosporophylls (carpels) are joined up, and the 
ovules are in a closed chamber, the ovary. 
Stamens of Lhe stamens, as in the Gymnosperms, contain 
Angiosperms. the pollen grains, but there are four pollen-sacs 
instead of two, as in Pinus. When fully developed the wall 
of an anther shows an external epidermis with a well-marked 
cuticle, and within this a layer of cells with fibrous thickening. 
At a certain point in the wall, opposite the partition between 
the two pollen-sacs, the cells are smaller and the thickening is 
absent ; this is the point of dehiscence of the anther. When 
the anther is ready to dehisce, the partition between the two 
pollen-sacs of each anther-lobe breaks down at this point of 
dehiscence, and thus the wall is ruptured. Dehiscence generally 
takes place by a longitudinal slit, sometimes by a transverse 
slit or by pores. 
Ovule of The structure of the ovule of an Angiosperm is 
Angiosperms. very similar to that already described in Pinus, 
