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MR. G. MASSEE ON A FRESHWATER ALGA. 



































intact, and thus forming one growing-point only instead of four. 

 In all multicellular algae the stem-like base eventually disappears, 

 but in the following genera, which are all freshwater forms, the 

 attenuated and often elongated basal portion is permanent, 

 hence the species are described by systematists as being 



" stipitate " : 



Characium, A. Braun ; Hydrianum, Rab. ; Sciadium, A. Braun 

 (Sciadium is included as a section of the genus Ophiocytium by 

 Eabenhorst) ; Peromelia, Gobi ; Actidesniium, Reinsch ; Dictyo- 

 sphcerium, Nag. ; Coelastrum, Nag. ; Dimorphococcus, A. Braun ; 

 Afischococcus, Nag. ; Cosmocladium, Breb. ; Dactylococcus, Nag. ; 

 Oocardium. Nag. 



The following genera form a transition from permanently 

 stipitate to sessile forms: — Apiocystis,lX'&g. ; Hydrocytiurn, A. 

 Braun ; Codiolum, A. Braun. 



In the Diatomacece stipitate genera are numerous, but the 

 stem differs from the type already described in being from the 

 first solid, and not an attenuated condition of the cellulose cell- 

 wall, as in the stipitate forms of freshwater algae. 

















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EXPLANATION OF PLATE XII. 



Fig. 1. Dictyosphcerium Ehrenbergianu 



3. 

 4. 



ft. 



(5. 



7. 



8. 



9. 



600 



600 



2. The same, at a later stage, with a mucilaginous sheath. X 

 The same, showing the earliest stage of fission. X 600. 

 The same, showing the first four divisions of the cell in the act of 

 dividing, x 600. 



Peripheral portion of same, showing the swollen apices dividing in a 



dichotomous manner, x 600. 

 Portion of same, showing the extent of division undergone by one of the 



gments 



X 3f>0. 



Portion of same, showing the escape of a zoospore from its parent cell 

 X 1200. 



Zoospore of same, x 1200. 



Surface view of an individual cell involved in mucus, at end of vege- 

 tative phase, x 200. 













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