148 Chlorophycex 



Green Algae that their classification now rests upon a much more certain basis 

 than at any previous time. In fact, notwithstanding the large amount of 

 work yet remaining to be done, more particularly among the lower types, 

 it is unlikely that subsequent discoveries will involve any considerable change 

 of principle. The most important result of this recent work is the recog- 

 nition by the more experienced of algological investigators that the various 

 groups of the Green Algse have originated by a progressive evolution, either 

 directly or indirectly, from flagellated ancestors, and that the cytological 

 structure of the motile zoogonidia furnishes a reliable key to phylogenetic 

 relationship. 



Following up the suggestion of Bohlin ('97) that certain of the Green 

 Algae, by reason of their cytological structure, formed a very natural group 

 which should be embraced in the ' Confervales ' of Borzi ('89), Luther ('99) 

 discovered that in all cases when these Algje had been carefully examined 

 the zoogonidia had 'been found to possess two unequal cilia. He also 

 pointed out that this was the case in certain Flagellate forms in which the 

 cytological structure was very similar. He therefore proposed to remove 

 all these AlgaB from the Chlorophyceae and place them in a group of equal 

 standing which he named the ' Heterokonta?.' He brought forward at the 

 same time considerable evidence to show that this group possessed other 

 definite cytological peculiarities, and most probably had a direct Flagellate 

 ancestry. 



Bohlin ('01), in a very suggestive paper on the phylogeny of Green Alga3, 

 attempted to trace each of the principal groups back to an independent origin 

 from the Flagellata. His suggested classification was as follows : 



Heterokontee. 



A. Confervales. 



Families : (Chloramcebaceee) ; Chlorosaccacese ; Chlorotheciacese ; Confer- 

 vaceae ; Botrydiacese. 



B. Vaucheriales. 



Families : (Vacuolariacese) ; Vaucheriacese. 



Chlorophycese. 



A. Conjugates. 



Families : Desmidiaceae ; Zygnemacese ; Mesocarpacese. 



B. Siphoneae. 



Families : Codiacese ; Caulerpacese ; Bryopsidacese ; Dasycladacese ; Valoniaceae ; 

 Cladophoracese ; Sphseropleaceae. 



C. Protococcoidese. 



Families : Hydrodictyaceee ; Volvocineae ; Chlamydomonadineae ; Protococ- 

 cacese ; Tetrasporacese ; Oocystaceae. 



D. Ulotrichales. 



Families: Ulvacese ; ?(Stichococcace8e) ; Ulotrichaceae (incl. Cylindrocapsa) ; 

 Ctenocladacese ; Coleochsetacese ; ? Chroolepidacese. 



