THE AMERICAN BOTANIST 



87 



is easy; for the alveolation of the cell-protoplasm with conse- 

 quent increase in cell- volume, the primitive chromoplasts, and 

 the primitive nucleus are simple steps to make ; and the varieties 

 of colonial (filament) organization offer no difficulties of 

 interpretation. 



Again, one of the flagellated nitrifying bacteria (Nitro- 

 monas) serves best as an introduction to the flagellate type 

 of cell ; for in the first place, there is hardly question but that 

 flagellation historically preceded the other specializations of 

 the Chlorophyceae, and, in the second place, such a simple type 

 presents only the one new characteristic upon which we wish 

 to concentrate attention. All the problems connected with 

 locomotion may be treated here elementarily, yet satisfactorily. 



Chlamydomonas is a next selection as exemplifying the 

 origin of the great Chlorophycean group. Here the discussion 

 of the alveolation of protoplasm, the specialization of the hence- 

 forth indispensable auxiliary, chlorophyll, and the significance 

 of the nucleus and its phenomena, may all be taken up. Indeed, 

 it seems to me most urgently advisable (and class-room exper- 

 ience justifies the conclusion) tO' thrash out each problem in the 

 earliest type in which it appears, rather than wait till we reach 

 the complex types. Chlamydomonas, moreover, serves as an 

 ideal introduction to the sex-problem in plants, and the evolu- 

 tion of the pure isogamy found here will warrant considerable 

 space of lecture-energy. 



For a type in which the advent of the walled, non-motile 

 stage is indicated — yet in simpler form than the fillament- 

 organization — Tetraspora, will serve. The significance of the 

 cellulose restraint upon all later plant life is to be stressed here. 



Ulothrix is always an admirable introduction to the fila- 

 ments — and to the fourfold zygote division that apparently 

 instituted the later sporocarp and sporophyte. Stigeoclonium, 

 in other respects like Ulothrix, exemplifies the origin of the 



