Phytogeny 27 



Luther and Bohlin have recently advocated considerable 

 changes in the classification of the Green Algse, most of which 

 have been rendered necessary by the abolition of the old artificial 

 group of the ' Confervoidege.' I agree with Bohlin in the estab- 

 lishment of the order ' Microsporales,' even though it appears to 

 be giving undue prominence to a small group of more or less 

 insignificant Algse, because species of the genus Microspora are 

 referable to no other order of green Algse. Likewise, the CEdo- 

 goniacese require placing in a separate order because of their 

 anomalous characters. 



Several of the recent students of freshwater Alga? have 

 attempted to show that all the main groups of the Chlorophycese 

 have had a separate origin from unicellular, motile, ciliated or 

 flagellated ancestors. This is no doubt a very helpful idea, but 

 like many other such ideas it can easily be carried too far. It 

 appears most probable that certain groups of green Algse have had 

 a direct origin from ciliated or flagellated unicells, but that in itself 

 is no proof that other groups have had a similar origin. There is 

 not a shadow of evidence in support of the direct and individual 

 origin of the Microsporacese, the Conjugata?, the Vaucheriacese, the 

 (Edogoniacese or the Cladophorales ; in fact, there is every reason 

 to suppose that some at least of these groups have originated from 

 previously existing filamentous forms. 



The origin of the Conjugate seems very uncertain. Black- 

 man, in his scheme of evolution 1 , and Bohlin 2 have both suggested 

 an origin from the unicellular motile Chlamydomonad-type, and 

 therefore directly from the Flagellata. To my mind this shows a 

 lack of experience of the Conjugata? as a whole, and particularly 

 of the family Desmidiacese. Whatever the true origin of the 

 Conjugate it cannot have been direct from Flagellate forms. 

 Presumably the first Conjugates which would arise from such 

 motile unicells would be themselves unicells, or loose aggregates of 

 cells. Now, such is exactly the condition found in the Desmidiacese ; 

 but it has been clearly shown 3 that the Desmidiacese is unques- 

 tionably a family of Conjugates derived by retrogression from 

 filamentous ancestors, and therefore, they cannot by any possible 

 means have had a direct origin from unicellular motile organisms. 



1 Blackman, I.e. p. 684. 2 Bohlin, I.e. p. 22. 



3 W. & G. S. West in Ann. Bot. xii, 1898, p. 55 ; G. S. West in Journ. Linn. 

 Soc. Bot. xxxiv, 1899, pp. 40941."). 



