The Angiosperms 153 



the gymnosperms. The male gametophyte is also 

 very similar to that of many gymnosperms. The 

 very slight change shown in the evolution of the 

 microspore is remarkable. There is little difference 

 structurally between the pollen-spore in the highest 

 seed-plant and the spore of the humblest liver- 

 wort. 



The development of the megaspore shows many 

 analogies with that of the gymnosperms, and the 

 early development of the female gametophyte is 

 very similar. The early stages of germination in 

 the embryo-sac are quite similar to those in the pine 

 or Selaginella; but the nuclear divisions are much 

 less numerous, so that in the normal embryo-sac, at 

 the time it is fertilized, there are only eight nuclei, 

 representing as many cells, of the extremely re- 

 duced female gametophyte; or in some cases there 

 may be only seven nuclei, as there is a fusion of two 

 of the original nuclei (Fig. 16, C). 



There has been much discussion as to the homolo- 

 gies of the structures of the embryo-sac in gymno- 

 sperms and angiosperms, and the matter is still in 

 dispute. The most marked departures from the 

 ordinary angiospermous type are found in two 

 plants which are in some respects very unlike. In 

 the genus Peperomia, a simple dicotyledon which 

 in some ways suggests some of the lower mono- 

 cotyledons, the gametophyte has sixteen instead of 

 eight nuclei, and this is true also in Gunnera; and 

 in the screw-pine (Pandanus), a monocotyledon, 



