Fig. 178.
Antheridia of Fucus,
on branched threads.
366. Fertilization.—At maturity the spermatozoids and egg-cells float outside of the oval cavities, where fertilization takes place. The spermatozoid sinks into the protoplasm of the egg-cell, makes its way to the nucleus of the egg, and fuses with it as shown in [fig. 181]. The fertilized egg then grows into a new plant. Nearly all the brown algæ are marine.
Fig. 179.
Antheridia of Fucus with
escaping spermatozoids.
Fig. 180.
Eggs of Fucus surrounded
by spermatozoids.
Fig. 181.
Fertilization in Fucus; fn, female nucleus; mn, male nucleus; n, nucleolus. In the left figure the male nucleus is shown moving down through the cytoplasm of the egg; in the remaining figures the cytoplasm of the egg is omitted. (After Strasburger.)