7C 



EIGHTEENTH REPORT. 



cells. The perinaueiit geueration, or the plant body, of the Moss 

 or Liverwort consists of cells with haploid nuclei. The zygote by 

 its division i)roduces the mass of cells with diploid nuclei, some 

 of which remain sterile and have protective or assimilative func- 

 tions while others become the spore mother cells within which, 

 after meiosis the four nuclei become the spore nuclei. Because in 

 the Ferns this sporogenous structure that arises from the zygote 

 has an independent existence as a distinct generation botanists 

 usually apply the terms gametophyte and sporophyte to the main 

 plant body and the sporogenous structure respectively, of the Bryo- 

 phyta also. 



7 S 



Figure 7. Sexual cycle of Mosses and Ferns. SP=Point of spore production. 

 Figure 8. Sexual cycle in the Flowering Plants. 



In the Ferns the sexual generation, the gametophyte, is the short- 

 lived one, and the sporophyte long-lived. Otherwise the sexual 

 cycle is the same as for the Br^^ophyta (Fig, 7). Very incorrectly 

 these two generations are often spoken of as the sexual and asexual 

 generations respectively. I have tried to point out that the re- 

 reduction division is as important part of the sexual cycle as the 

 cell and nuclear union. The sporophyte is merely a further de- 

 velopment of the comparatively few-called structure that arises 

 from the zygote in Nemalion and produces the carpospores: (I do 

 not want to be misunderstood as holding that Nemalion is a direct 

 ancestor of the Ferns or Mosses, but I mean that a further develop- 

 ment of the same idea that appears in Nemalion gave rise to the 

 sporophyte in these groui)s). The true asexual reproduction is 

 that by which tlie same generation is perpetuated, not that repro- 



