92 EVOLUTION OF PLANTS. 



infusoria. Active, mostly bi-ciliate cells, showing both 

 animal and plant characters. 



From the active vol vox cell, protococcus-like forms 

 probably arose, unicellar non-motile cells, but revert- 

 ing at times to the active condition. 



Next higher in rank the confervoid algae. These 

 may have arisen from protococcus forms by the cells 

 remaining together after fission had occurred. Simpler 

 forms unbranched, e. </., conferva ; or branched, e. g., 

 cladophora. These also produce at times volvox-like 

 ciliated cells. < 



Evolution of sex. In the simplest forms the whole 

 unicellular individual is at once vegetative and re- 

 productive. At first reproduction effected by simple 

 fission, purely non-sexual. In simplest form of sexual 

 reproduction two individuals fuse into one. Next 

 there is a difference in the size of the two individuals ; 

 the larger, the female ; the smaller, the male. A step 

 higher, the female cell loses the power of motion, 

 and remains passive in a special cell (oogonium), 

 where it is fertilized by the active male cell. 



Algae and fungi. Fungi a specialized group of ob- 

 scure origin ; throw no light on the origin of the 

 higher plants. 



Algae green, red, brown. The former a generalized 

 group from which the others have probably sprung ; 

 the others highly specialized, mostly marine forms. 

 The green algae mostly fresh water forms, arid import- 

 ant as the progenitors of the higher land plants. 



