REPRODUCTION IN PLANTS 



111 



Thus it is clear that the gametophyte generation of Flower- 

 ing Plants is reduced to practically its lowest terms a few 

 nuclear divisions sufficient to form the gametes. The whole 

 generation is telescoped, as it were, within the flower of the 

 previous sporophyte generation, so that sporophyte seems 

 to produce sporophyte; whereas, as a matter of fact, three 

 distinct generations contribute directly to the formation of 

 the seed. A seed is really a highly modified megasporangium 

 with its contents. The seed coat comprises tissue from the 

 megasporangium of the parent sporophyte bearing the flower 

 (first generation). Certain nutritive tissues (endosperm) 

 represent the female gametophyte (second generation). The 

 product of the fertilized egg is 

 a young sporophyte (third 

 generation). (Fig. 62.) 



The great reduction of the 

 gametophyte generation in 

 Flowering Plants is accom- 

 panied by a transference of 

 some of the phenomena associ- 

 ated with sexuality to the 

 sporophyte, so that the latter, 

 though intrinsically asexual, 

 comes secondarily to exhibit 

 certain sexual characters, chiefly in the flower. Thus, 

 although the stamens and pistil (carpels) are actually 

 sporophylls of the non-sexual generation, they are frequently 

 referred to as the male and female organs of the flower. 

 Likewise POLLINATION, or the transference of the pollen 

 grains from anther to stigma, is often called the fertiliza- 

 tion of the flower; whereas, as we have seen, it is merely a 

 preliminary step which makes it possible for gametophytes 

 to meet on common ground so that the sperm, which them- 



FIG. 62. Seed of a Violet. At the left 

 the hard seed coat ; at the right, a section 

 showing the abundant endosperm (female 

 gametophyte) enclosing the embryo, or 

 young sporophyte. (From Coulter.) 



