SEED 457 
middle of June of the second season and fertilization soon follows. 
In addition to its simplicity the notable features of the male 
gametophyte are that the sperms have no cilia and that they are 
conducted to the archegonia by the pollen tube. 
Seed. — The fertilized egg at first forms tiers of cells, which 
constitute a long filament, called a suspensor, at the end of which 
the embryo develops deeply imbedded in the nutritive tissue of 
the female gametophyte. When mature the embryo is still 
surrounded by much gametophytic tissue called endosperm. 
While the embryo or the young sporophyte is developing, the 
ovule and the entire cone continue to enlarge. The integument 
is transformed into a seed coat, and when mature the seed sepa- 
Fic. 406. — Diagram of the life cycle of the Pine. Starting with the tree 
at the left, the two kinds of strobili are shown at a and b, the two kinds of 
sporophylls and their sporangia at c and d, the two kinds of spores at e and f, 
the gametophytes at g, the mature seed at h, from the embryo of which a 
new tree develops. 
rates from the ovulate scale with a long membraneous wing, 
which enables the seed to float in the air (Fig. 405.) Pine 
seeds, although usually smaller, are similar in general structure 
to the seeds of Cycads. They contain a female gametophyte 
bearing a young sporophyte and a protective covering composed 
of the integument and the nucellus, the latter persisting as a 
membrane about the gametophyte or endosperm. 
The scales of the ovulate strobilus continue their development 
until the seeds are mature and remain tightly closed so that the 
seeds are well protected. After the cone is mature, the scales dry 
