450 SPERMATOPHYTES (SEED PLANTS) 



number, are produced at the uiicropylar end, and have much 

 shorter necks and are simpler in other ways than the archegonia 

 of Pteridophytes. The eggs are large and the most conspicuous 

 part of the archegonia. A section through an ovule ready for 

 fertilization looks like the one shown in Figure 399. 



Male Gametophyte. — The microspores or pollen grains, as they 

 may now 1)0 called since they have to be transferred to the ovule 

 before they can function, usually contain three-celled gameto- 

 phytes at the time of their shedding, and in this condition they 

 reach the megasporangium, pass through the micropyle, and reach 

 the pollen chamber, where they are in contact with the beak of 

 the nucellus. In this position the three-celled gametophyte, 

 which consists of a vegetative, generative, and tube cell, com- 

 pletes its development. The miscrospore develops tubes which 

 branch and penetrate the beak of the nucellus in various direc- 

 tions, and function as absorptive structures. Finally, the beak 

 of the nucellus breaks down and thereby a passage way to 

 the archegonia is provided. Meanwhile the generative cell 

 enters one of the pollen tubes and passes farther into the pollen 

 chamber where it divides, forming a stalk cell and a body cell, 

 the latter of which forms the sperms, usually two in number. 

 The sperms bear a large number of cilia, and after escaping from 

 the pollen tube they swim through the watery solution present 

 in the chamber and thereby reach the archegonia and finally the 

 eggs. 



Thus, when the male gametophyte is mature, it consists of only 

 four -cells besides the sperms, and there is no structure formed that 

 resembles an antheridium. In addition to the absence of an 

 antheridium, it should also be noted that pollination and the 

 growth of tubes are other new features which occur in connection 

 with the male gametophytes of Cycads. It is obvious that the 

 introduction of pollination and the growth of pollen tubes must 

 accompany the permanent enclosing of the female gametophyte 

 in the megasporangium. 



Seed. — The seed is another new feature of the Cycads. After 

 fertilization, a young sporophyte {embryo) is developed and is 

 pushed well down into the nutritive tissue of the gametophyte 

 by a filament of celh (suspensor). During fertilization and the 

 development of the embryo, the ovule continues to grow and 

 the integument becomes pulpy, while the outer region of the re- 



