DEVELOPMENT OF PLANTS 



339 



With one exception this is the only group characterized by this 

 peculiar germination which is more suggestive of the growth of 

 the animal egg where a large portion of the egg is reserve food 



D 



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

 archegonium at time of fertilization. One of the male gametes, o", is seen 

 fusing with the female, ?. The second male gamete, J", 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, c, into the tissues of the female gametophyte. — A after 

 Ferguson; B-E after Coulter and Chamberlain. 



for the nourishment of the embryo. The nourishment of the 

 female gamete by the jacket cells is also suggestive of certain 

 animals in which the egg cells are formed in a similar manner. 

 The embryo is developed from the uppermost plate of cells which 

 are pushed into the cells of the gametophyte by the elongation 

 of the suspensory cells just below them (Fig. 255, E). Each of 

 these four cells may form an embryo (Fig. 256, 2), but usually 

 only one develops. The mature embryo consists of a stem bear- 

 ing two or several laterally-placed cotyledons and a root with 



