DEVELOPMENT OF PLANTS 32; 



of the numerous tube cells, the tissues above the archegonial 

 chamber become disorganized and absorbed so that the end of 

 the gametophyte containing the gametes hangs down into the 

 cavity thus formed and comes into close proximity to the arche- 

 gonial chamber (Fig. 246). At this stage of development the 

 archegonial chamber has become filled with water. 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 and finally 

 enter the archegonia, as in the case of ferns. 



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 directly by 

 division and not as in the ferns, through the reorganization of 

 the contents of the cells into gametes which are set free through 

 the mucilaginous modification of the walls of the mother cells. 

 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 are 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 

 rudimentary root, stem and two cotyledons (Fig. 248, C). In 



