4o6 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. ^ 



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, 



' The accomplishment o£ fertilization by the mediation of a pollen-tube 

 (siphon) is called siphonogamy. 



