Division 4. =Gymnospermæ.= The ovules, as well as the seeds, are borne
_naked_ on the surface of _open carpels_, or on the apex of a stem
(ovary wanting). The pollen-grains are conveyed by the wind to the
ovules, and caught by drops of mucilage, secreted by the micropyle.
A “stigma” is _wanting_. The entire _female prothallium_ (_the
endosperm_), which serves for the nourishment of the embryo, is _formed
before fertilisation_. The archegonia are _embedded in the upper part
of the prothallium. The pollen-grains are “multicellular,” i.e._ there
is always in their interior a distinct prothallium, formed by 1–3
cells, and a larger cell which gives rise to the pollen-tube.
Division 5. =Angiospermæ.= The carpels surround the ovules and form
an entirely closed chamber (_ovary_), in which the ovules mature and
ripen into seeds. The surface of a portion of the apex of the carpel
is transformed into the “stigma,” which, by a sticky fluid and also by
hair-structures, is capable of retaining the pollen-grains conveyed to
it by the wind, or more frequently by insects. The pollen-tube grows
from the stigma, through the “conducting cellular tissue” (_style_),
to the ovules. The pollen-grains contain two cells, a vegetative and
a free generative cell. The latter passes into the pollen-tube and
there divides into two, one of which is the sperm-nucleus. The female
prothallium, which is intended to serve as nutritive-tissue, is formed
_after fertilisation_. Archegonia are wanting.