Fig. 361.
Archegonium of white pine at stage of fertilization, en, egg nucleus; spn, sperm nucleus in conjugation with it; nb, nutritive bodies in cytoplasm of large egg; cpt, cavity of pollen tube; vn, vegetative nucleus or tube nucleus; stc, stalk cell; spn, second sperm nucleus: pr, portion of prothallium or endosperm; sg, starch grains in pollen tube. The sheath of jacket cells of the archegonium is not shown. (After Ferguson.)
626. Homology of the parts of the female cone.—Opinions are divided as to the homology of the parts of the female cone of the pine. Some consider the entire cone to be homologous with a flower of the angiosperms. The entire scale according to this view is a carpel, or sporophyll, which is divided into the cover scale and the ovuliferous scale. This division of the sporophyll is considered similar to that which we have in isoetes, where the sporophyll has a ligule above the sporangium, or as in ophioglossum, where the leaf is divided into a fertile and a sterile portion.
Others believe that the ovuliferous scale is composed of two leaves situated laterally and consolidated representing a shoot in the axis of the bract. There is some support for this in the fact that in certain abnormal cones which show proliferation a short axis appears in the axil of the bract and bears lateral leaves, and in some cases all gradations are present between these lateral leaves on the axis and their consolidation into an ovuliferous scale. In the normal condition of the ovuliferous scale the axis has disappeared and the shoot is represented only by the consolidated leaves, which would represent then the macrosporophylls (or carpels) each bearing one macrosporangium (ovule).
Fig. 362.
Pine seed,
section of,
sc, seed coat;
n, remains of nucellus;
end, endosperm
(= female gametophyte);
emb, embryo =
young sporophyte.
Seed coat and nucellus =
remains of old sporophyte.
Fig. 363.
Embryo of white pine
removed from seed,
showing several cotyledons.
Fig. 364.
Pine seedling
just emerging
from the ground.