DEVELOPMENT OF PLANTS 359 



cell usually divides but once forming two cells, in each of which 

 are organized two huge male gametes with spirally arranged 

 cilia (Fig. 247, C-E). Owing to the growth of the numerous tube 

 cells, the tissues above the archegonial chamber become dis- 

 organized and absorbed so that the end of the gametophyte 

 containing the gametes bends into the cavity thus formed and 

 comes into close proximity to the archegonia (Fig. 246). Owing 

 to the swelling of the cells (g) and (w) assisted also by the accu- 

 mulation of fluids in the tube, the male gametophyte is ruptured 

 at its basal or spore end and the male gametes are discharged into 

 the archegonial chamber where they swim about in the fluids 

 probably emitted from the tubes at the time of their discharge. 

 This fluid has been observed by Chamberlain to cause a shrinking 

 of the neck cells in one species of Dioon and so we see how the 

 male gametes may enter the archegonia. 



The most noticeable departure in the sexual generation of 

 the cycads is the very considerable reduction of the male game- 

 tophyte which consists of a delicate tube containing a few cells 

 from one of which the male gametes are formed as in the ferns. 

 You also notice that the gametophytes have become entirely 

 parasitic upon the sporophyte, the male gametophyte at first upon 

 the sporophyte which bore it and later upon the megasporangium. 

 Attention may be called to a suggestive departure in the develop- 

 ment of the female gametophyte that has been observed in one 

 of the cycads. In case fertilization is not effected, the gameto- 

 phyte ruptures the sporangium and projects as a green tissue, as 

 in certain heterosporous ferns. 



(c) Development of the Sporophyte. — The germination of the 

 gametospore differs in two important respects from the ferns. 

 Its nucleus gives rise by repeated divisions to numerous nuclei 

 which arrange themselves around the walls of the gametospore, 

 becoming especially numerous at its lower end, and finally form 

 cell walls (Fig. 248, A). This structure is called the pro-embryo. 

 From the lower cells of the pro-embryo is organized a massive 

 suspensor (Fig. 248, B), which pushes the outermost cells of the 

 pro-embryo deep into the tissues of the gametophyte where they 

 develop the young sporophyte or embryo, which consists of a 



