316 Causes and Course of Organic Evolution 



Valoniacese, and Dasycladiacese, it divided up into many 

 small chromoplasts each witli a pyrenoid body. 



In a sentence now we may sum up the distributional value 

 of the green algse — excluding diatoms and related organisms — 

 by stating that 167 genera and 1924 species are fresh-water, 

 while 59 genera and 391 species are marine. The two latter 

 numbers include also the great majority of the most complex 

 and modified species. 



The Brown x\lg8e or Phaeophycese can next be examined. 

 These are so thoroughly marine, and so advanced in structure, 

 that the task of connecting them ^^'ith ancient forms is con- 

 fessedly a difficult one. But suggestive connecting links seem 

 still obtainable. Tracing back origins for these, as for some 

 of the Green Algse, to the chamaesiphoneous Cyanophyceae, 

 most of the genera of the latter include species of a yelloTN'ish 

 or broTMi color. Further, while the majority of the species 

 are fresh-water and of bluish or violet-green tint, not a few 

 are marine and yellow-brown. 



But, amongst living members of the Phseophyceae, such 

 genera as Lithoderma and Heribaudiella (Engl. Nach., p. 174) 

 resemble, in growth of the plant individual, in cell structure, 

 and in the arrangement as well as in the formation of terminal 

 conidangia with conidiospores, such cyanophyceous genera 

 as- Pleurocapsa, Chamcesiphon, and Hyella, except that the 

 former are nucleate and give rise to sex cells, while the latter 

 have only evolving or diffuse nuclei, and are, so far as we know, 

 asexual. Phceococcus and PhcEothamnion too are interesting 

 fresh-water phaeophyceous genera, that in many points of 

 history recall the Cyanophyceae. The origin of the gamete 

 cells also in Phceococcus, as described and figured by Borzi 

 (99, 1: 14), indicates that formation of gamete cells \Wth lateral 

 cilia, so typical of the Bro^^^l Algae, may early have started 

 even amongst unicellular species. 



So we would regard the bulk of available evidence, even 

 though slight, as favoring a primitive and very remote origin 

 for the Brown Algae from fresh-water yellow or bro^^^l-green 

 ancestors of a cyanophyceous nature, and that early migra- 

 tion into littoral margins of varying depth accentuated bro^^'n 

 pigment production in the chlorophyll substance. Having 

 reached the shore area with its ceaseless wave-motions, its 

 changing mechanical strains, and its varying light intensities, 



