Evolution of Plants 323 



or bright green unicellular members of the same division the 

 Desmidese and higher green Conjugatse probably sprang, and 

 these have practically all retained a fresh-water environment. 

 From protococcaceous ancestors we have derived the Vol- 

 vocacese that are fresh-water and also represent the climax 

 of unicellular specialization. From some simple unicellular 

 greenish bro'wn fresh- water genus like Amphidiniiim, derived 

 in turn from pleurococcaceous ancestry, the four divisions 

 from Gynmodiniacese to Diatomacese have apparently arisen. 

 A large number of these, and the simplest genera of them, 

 are still fresh-water, but many have permanently become 

 marine livers. These last have given rise to many and varied 

 marine species, but have failed to evolve liigher organisms 

 than themselves. 



But, from fresh-water ulvaceous, cladophoraceous, and 

 siphoneous divisions, migrants shoreward originated the abun- 

 dant genera and species of green marine algse, which failed 

 however to originate higher organisms than themselves. On 

 the other hand the Aphanochsetacese and Coleochaetacese 

 amongst higher fresh-water algse have been regarded as related 

 to ancestral organisms, from which the primitive Bryophyta 

 and Pteridophyta have probably originated, whose morpho- 

 logical continuity we shall endeavor to ^ trace in the next 

 chapter. 



The probable origin of the bro'^.vn seaweeds has been traced 

 from a yellow-brown chamsesiphoneous ancestry, through 

 fresh-water genera like, or allied to, Phceococcus and Phceotham- 

 nion^ on to marine derivatives of increasingly advancing struc- 

 ture, and that ramified into a wealth of species, but failed to 

 evolve higher organisms than those of the class. From blu- 

 ish, purplish, or pink Cyanophycese of fresh-water habitat, 

 the red seaweeds have started, for connecting genera that 

 are now alive serve well to link all into a continuous organic 

 chain. But while most of the simplest groups are mainly 

 fresh-water, or still retain some representatives there, diverging 

 lines from some of these early took on a marine existence, 

 assumed a fixed red or claret color, and i)roduced a great wealtli 



