282 



Ulotrichales 



The inter-relationships of some of the branched forms of the Ulotrichales are rather 

 obscure, and Pascher ('07) has attempted to trace certain lines of descent by a survey of 

 the characters of the zoogonidia and gametes. 



The relationships of the unbranched genera are fairly clear, and the transition from 

 Geminella to Ulothrix, through Stichococcus, is obvious and complete. Binuclearia and 

 Uronema are both specialized forms closely akin to Ulothrix. Rhaphidonema may be 

 a specialization from the subaerial form of Stichococcus or a reduction from the subaerial 

 forms of Ulothrix. 



It is highly probable that there have been several divergent lines of descent from members 

 of the Ulotrichaceae, along three of which oogamy has been independently attained. 



The accompanying diagram may help the student to form an approximate idea of the 

 phylogenetic relationships of the chief types of the Ulotrichales. 



APHANOCH^ETACE^E 



Aphanochsete 



COLEOCH^ETACEiE 



Coleochgete 



ITRENTEPQHLIACE.E 

 CH/ETOPHORACE.E ' 



\ Chsetophora 



Draparnaldia ^ 



Acrochaete 



Stigeoclonium 



Ulvelleee 



Microthamniete 

 Gomontiete 



Chsetonema 



/ 



CYLINDROCAPSACE.E 



Cylindrocapsa 



\ 



Ulothrix 

 A 



Binuclearia 



MICROSPORACE^E 



Microspora 



Radiofilum 



Stichococcus 



Uronema 

 Rhaphidonema 



\ 



Catena 



ULOTRICHACEAE 



Psephotaxus 



Geminella 



Ancestors in the Protococcales. 



