REPRODUCTIVE CELLS. 155 



in Homosporous Pteridophyta, and those of the female pro- 

 thallinm in the macrospore of Heterosporous Pteridophyta. 



In the Bryophyta an apparent anomaly is encountered, for it 

 is not, as would at first appear, the moss-plant (Musci) whicli is 

 the sporophyte, but a rudimentary mass of cells, the sporogonium 

 and sporogenous cells. The gametophyte, or product of ger- 

 mination of the spore is here a much more highly differentiated 

 plant than the sporoph3te, and in Musci forms the moss-plant 

 proper. In the Hepatic^, the sporophyte and gametophyte 

 are, as in the Musci, fused in the one plant, a sporogonium 

 being produced, which corresponds to the sporophyte, or asexual 

 generation. Germination of a spore produced in the sporo- 

 gonium results in tlie formation once more of the protonema, from 

 which arises the moss-plant or Liverwort proper (gametophyte, 

 or sexual generation). 



In the Thallophyta, the homologies become somewhat limited. 

 The antheridia and oogonia are, of course, homologous structures 

 to those found in the Bryophyta and Pteridophyta, but beyond 

 this it becomes very difficult to trace their reproductive relations, 

 although attempts have been made to do so. 



Certain divergencies from the main type of maturation of the 

 embryo-sac in Angiosperms are sometimes met with. Thus, in 

 Peperomia, the primary nucleus of the embryo-sac divides into 

 sixteen, instead of eight nuclei, and these are uniformly distri- 

 buted through the cytoplasm, instead of forming an egg-apparatus 

 (synergidse and egg-cell) and antipodal cells. No polar nuclei arc 

 met with in this case. 



In Sparganium simplex, the antipodal cells di\ide many times, 

 and give rise to a mass of one hundred and fifty, or even more, 

 cells; in this plant also a prothallial cell is met with in the 

 microspore. These instances are interesting, as they point to a 

 sort of re\'ersion to ancestral processes. 



Parthenogenesis, or the development of an unfertilised egg- 

 ceil, is known only in the case of Chara crinita (Algae). Tlie 

 development of parthenogenetic eggs is more common in the 

 animal kingdom, notably in the case of D(.qiliniu (water-floas). 



