No. :><)(> | 



HOTEL 



AM) LITERATURE 



101) 



ductive organs with arehegonia and antheridia. hut would not 

 be willing to go so far as to hold that the latter have been 

 derived directly from the former. 



There follows then in Schenck's paper an attempt to homolo- 

 gize the spore mother cell of the archegoniates with the tetra- 

 sporangmni of the Dictyotaceae, based on the fact that the mitoses 

 in both cells are reduction divisions terminating the sporophytic 

 phases of life histories with an alternation of generations. The 

 endogenous formation of spore mother cells in the archegoniates 

 is regarded as an ecological adaptation associated with terrestrial 

 life habits. The analogy is perfectly clear, but it may well be 

 questioned whether it suggests so close a relationship as to 

 justify an homology, especially since reduction phenomena are 

 now known for a number of unrelated groups of algae and fungi. 

 The tetraspore mother cell of the red alga? is probably in most 

 forms also the seat of chromosome reduction terminating a sporo- 

 phytic phase. The mitoses in the zygote of Spirogyra have 

 recently been shown by Karsten to be reduction divisions, as has 

 been suspected, and it is altogether probable that similar reduc- 

 tion mitoses will be found to occur with the germination of the 

 eggs of CEdogonium and a number of other alga?, and for certain 

 phycomycetes as well. All of these cells in being the seat of reduc- 

 tion mitoses are analogous to the spore mother cells of arche- 

 goniates, but that would not warrant their being considered as 

 homologous with the latter structures. There is, on the contrary, 

 good reason to believe that in plants reduction phenomena became 

 established as features in the life histories of a number of groups 

 quite independently of one another, as the evidence indicates was 

 also true of the processes of sexual evolution and the differen- 

 tiation of sporophyte generations. Chromosome reduction as a 

 Physiological process seems to be a corollary of sexual nuclear 

 fusions, but the cells concerned in the former are less likely to 

 be homologous with one another than the cells concerned in the 

 latter, since they are a part of a new phase which tends to become 

 elaborated as the intercalated sporophytic generation. It is clear 

 that a number of types of gametes throughout the plant kingdom 

 are not homologous, and equally clear that several different forms 

 of cells associated with chromosome reduction are not homologous. 



Finally, Schenck compares the gametophytes and sporophyte 

 °f the archegoniates with the thalli of the brown alga?, but it 

 w doubtful whether he really strengthens his case. The resem- 

 blance of the gametophytes of thallose liverworts to band-shaped 



