Phylogeny of Isokontx 



159 



line of evolution has resulted in no Green Algae of importance, and like the 

 Volvocine series has not emerged from the confines of the Protococcales, unless 

 Blackman's suggestion as to the origin of the Siphonales is a correct one 

 (see p. 223). The tendency to retain the unicellular or unseptate form in 

 the adult plant and to restrict multiplication entirely to small motile cells 

 is found in the Chlorochytriese, Dicranochaeteae, Characieae and Halosphserieae. 

 These small groups have therefore been placed alongside one another in the 

 family Planosporaceae. A similar multiplication. also occurs in the ccenobic 

 Hydrodictyaceae. 



The evolutionary lines within the Protococcales may be represented as 

 follows : 



Higher Isokontae 



Palmellaceae 



3 



o 



o 



Chlamydomonas 



A careful consideration of our present knowledge of the Isokontae leads 

 one to the conclusion that there are only six natural groups into which it 

 can be divided. These groups, both for convenience and for the sake of 

 consistency, are here termed ' orders,' and are as follows : 



Order 1. Protococcales. 



2. Siphonales. 



3. Siphonocladiales. 



4. Ulvales. 



5. Schizogoniales. 



6. Ulotrichales. 



