Botanists were for a long time content to know that the scattering of the pollen from the anther, and its application to the stigma, were necessary for the production of perfect seed, but the stages of the process of fertilization remained unexplored.
In rare cases the oosphere has been known to germinate without fertilization (Oedogonium, Cylindrocapsa).
The closed ovary implies a mode of fertilization which is profoundly different, and which was probably correlated with a simultaneous development of insect life.
After fertilization the equivalent of the oospore divides directly to form a group of carpospores.
The endosperm detached from a large Ginkgo ovule after fertilization bears a close resemblance to that of a cycad; the apex is occupied by a depression, on the floor of which two small holes mark the position of the archegonia, and the outgrowth from the megaspore apex projects from the centre as a short peg.
A double fertilization thus takes place.
These illustrations are comparatively simple; it would have been easy to select others of a more complicated nature, but all evidently connected with the visits of insects and the cross fertilization of the flower.
Such plants are called dimorphic. Other plants are timorphic, as species of Lythrum, and proper fertilization is only effected by combination of parts of equal length.
The spermatogenesis and maturation and fertilization of the germ-cells present nothing out of the common and need not be C.
Sexes separate, fertilization by spermatophores.