DEVELOPMENT OF PLANTS 



371 



arose at first as an absorbing organ to supply the antheridial cell 

 with food, as is the case in the cycads. In the more advanced 

 types the archegonia became more effectually enclosed in the 

 sporangial tissues and the tube cell assumed in addition the 

 function of a conduit for the male gametes which lost their 



^^&X 



D 



Fig. 255. Development of the pro-embryo of pine: A, section of an ar- 

 chegonium at time of fertilization. One of the male gametes, d^, is seen 

 fusing with the female, 9. The second male gamete, cf, the tube nucleus, 

 and the wall cell are also shown near the neck of the archegonium. B, the 

 gametospore has germinated, forming four cells, which are passing to the 

 upper end of the sac. C, the cells shown in B, arranged at end of sac and 

 in process of division (only two cells in this sectional view). D, later stage, 

 the pro-embryo of four plates of cells. E, the second plate or suspensory 

 cells, s, of the pro-embryo elongating, thus pushing the embryo-forming cells, 

 e, into the tissues of the female gametophyte. — A after Ferguson; B-E after 

 Coulter and Chamberlain. 



motility as a result of this new method of transport to the 

 female gamete. 



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

 gametospore of the pine will illustrate the more important 

 features in the process. The nucleus of the gametospore divides 

 a varying number of times, commonly forming four nuclei (Fig. 

 255, B), which pass to the upper end of the spore and arrange 



