ALG^E 77 







but these are more properly aggregates or colonies of 

 unicellular units than individual plants. The repro- 

 ductive cells of the Protococcacese are always very 

 primitive in character, and usually are motile, much 

 like their unicellular volvocineous ancestors. The 

 third line of development, represented by the Confer- 

 vacese, may be assumed to have arisen from the lower 

 Volvocinese through the simpler Protococcacese, with 

 which they agree closely in their development. The 

 origin of the typically multicellular Confervacese from 

 the unicellular Protococcacese has been brought about 

 by the cohesion of the cells after fission is complete. 

 By repeated divisions in a single plane the simpler 

 filament of the lower Confervacese may thus be assumed 

 to have arisen. 



The differentiation of the plant body first resulted in 

 the establishment of a basal and apical region in the 

 unbranched filament, and, later, there arose branched 

 forms or a flat thallus. The development of the repro- 

 ductive parts parallels very closely that of the Volvo- 

 cinese, but the sexual cells in the higher types are borne 

 in special organs, antheridia and oogonia. 



The genus Coleochsete is the most specialized mem- 

 ber of the order, and in the formation of a rudimentary 

 spore-fruit (sporophyte) suggests a possible relationship 

 with the lowest mosses. 



The three orders- -Volvocinese, Protococcacese, and 

 Confervacese- -form, then, a continuous series leading 

 up to the higher plants, while the other algse are to be 

 considered as offshoots of the main stock. Of these, the 

 Siphonese have, perhaps, had a multiple origin, the sim- 

 plest one being related to the lowest Volvocinese or 



