406 STRUCTURE AND LIFE HISTORIES 
of the spermatozoid body may be considerably extended 
as a blunt point in pushing between two obstacles. The 
whole body seems flexible and changeable in the highest 
degree and is eminently fitted for its difficult task of finding 
and swimming through the narrow passage between the 
neck-cells of the archegonia." 
A point to be specially noted here, is that while a pollen- 
tube is introduced in the process of fertilization, the final 
act is accomplished as in lower aquatic forms, by the 
swimming of the sperms through liquid. The pollen- 
tube alone, as in higher plants, should suffice in Cycads to 
bring the sperm to the egg, and the retention of locomotion 
of the sperm, after the appearance of the pollen-tube, can 
be interpreted only as the persistence, by inheritance, of a 
character that was a fundamental necessity in lower 
forms. 1 
360. The Seed. During the processes of germination of 
the pollen-grains and fertilization, the ovule is increasing 
in size, and developing different tissues and juices. The 
outer wall of the nucellus hardens, while the integument 
becomes succulent and pulp-like, so that externally the 
structure resembles a plum. It cannot, however, be com- 
pared to a plum in morphology (i.e., cannot be homologized 
with a plum), for a plum is a ripened ovary, while the 
so-called "fruit" of the Cycads is a ripened ovule or 
seed. 
361. The Embryo. After fertilization the oosperm 
develops into an embryo-sporophyte (Fig. 302). This is 
often delayed until after the seed is planted, so that after 
the embryo has once begun to form it continues to grow, 
1 The accomplishment of fertilization by the mediation of a pollen-tube 
(siphon) is called siphonogamy. 
