Phylogeny 25 



has only succeeded in producing the elaborate but puny mockery 

 of them which we find in Gaulerpa" 



It is now necessary to trace the further developments from the 

 Palmellacea?, which family was the first result of the influence of 

 the Tetrasporine tendency on the Chlamydomonad-type. 



The Protococcacese is a group which has been gradually evolved 

 from the Palmellacese by the direct production of the unicellular 

 motionless stage with a firm cell-wall as the principal state of the 

 plant, the zoogonidia and the Tetraspora-skSige being only tran- 

 sient conditions in the life-history, and often absent. In the lower 

 forms of this family the cells are globose with firm cell- walls, and 

 all their reproductive processes show a marked tendency to trans- 

 form the motile elements into resting spores. In some of the 

 other forms of the family the cells exhibit great variety of form 

 (e.g. Oocystis, Nephrocytium, Kirchneriella, Chodatella, etc.), and 

 reproduction is largely by a type of spore termed by Chodat an 

 autospore. Such spores are usually produced in fours inside the 

 mother-cell, and at the moment of their liberation they possess 

 the exact form and external peculiarities of the mother-cell. 

 Sometimes the autospores are quite free after their liberation 

 (e.g. Lagerheimia, Oocystis), but at other times they are sur- 

 rounded by a gelatinous envelope (e.g. Kirchneriella, Nephrocy- 

 tium\. When the autospores are united together in a colony at 

 the time of their expulsion an auto-colony is produced. Such is 

 the usual method of multiplication of Scenedesmus. Forms of the 

 nature of Ccelastrum and Sorastrum have originated from the 

 lower Protococcaceffi with autospores, the latter being grouped 

 together into a globular auto-colony. 



The position of the two genera Pediastrum and Hydrodictyon 

 is still very doubtful. I am inclined to agree with Chodat that 

 the resemblance is due to convergence rather than to a common 

 origin. In Pediastrum the swarming stage is outside the mother- 

 cell and the new cosnobium arises by the apposition of motile 

 zoogonidia. In Hydrodictyon the new coenobium also arises by 

 the apposition of zoogonidia which have become quiescent, but is 

 formed inside the mother-cell. Both genera consist of coenobia 

 of ccenocytes, and for the present they are best kept in the 

 separate sub-families of the Pediastreae and Hydrodictye;c. 



Among the Chretophorales it is clear that the Ulotrk'hare.-r 

 have had a direct, origin from the Palmellacere through such forms 



