Siphonocladales 



Ulothrix 



Parenchymatous type 

 Ulvales 



Siphonales 



Oogamous type 

 Coleochaete 



branched heterotrichous 

 type, Stigeoclonium 



t 



Protoslphon 



t 



Chtamydomonad type 



Spherical 

 colonies 

 Volvocales 



Palmella type 



Scheme B 



In 1 95 1 Papenfuss propounded a third scheme for the Chloro- 

 phyceae in which the Volvocales represent the key position (scheme 

 C). 



Chaetophorales 



Parenchymatous T 



types Ulva ' 



Ulotrichales 



Prasiola 



Oedogonia 



Siphonales 



Other 

 Siphonocladales 



\ 



Cladophoraceae 



\ 



Dasycladales 



Conjugales -< — ■ Volvocales >-Chlorococcales 



t 

 Chlamydomonad 



type 



Scheme C 



This scheme would seem to be unsatisfactory in respect of the 

 Oedogoniales, Conjugales and Prasiola. Also, for reasons stated 

 above, the Siphonales may not have been derived from the Chloro- 

 coccales, and, based on scheme D, it is believed that a better series 

 of forms can be envisaged in the evolution of the Siphonocladales 

 from a Ulothricaceous ancestor. The details of the suggested 

 evolutionary development from the simple Ulothricaceous fila- 

 ment to the parenchymatous forms on the one hand and to the 



310 



