Evolution of Plants 317 



wide dispersal and steady though varied modification must 

 have occurred, till in the long-drawn interval between archsean 

 and present times there evolved those abundant species that 

 amount to 759, included in 145 genera. But these, unlike 

 some of the green algae, failed to develop higher and strongly 

 progressive descendants, so that they form a marine cul-de-sac 

 like many Ulvacese, the Valoniacese, the Rhodophycese, and 

 as we shall see later the Spongida, Echinodermata, and other 

 animal groups. 



In the restricted though steady evolution that they have 

 undergone, graded advances are sho^Ti in chromatophore and 

 in reproductive cell details, that are exactly paralleled by the 

 green algae. Thus, in the relatively simple Ectocarpaceae, 

 Encoeliacese, Chordariacese, and allies, the chromatophores 

 may vary from one large semi-cylindric of pale greenish yellow 

 hue to a few oval or strap-shaped ones, or to many that are 

 small lenticular and of deep orange color as in the highest 

 groups of the Fucacese and Laminariacese. 



Such advance in chromatophore condition is fairly well 

 correlated '^ith progress in sex cell differentiation, from union 

 of like ciliated gamete cells as in the above three first-cited 

 families, to the Cutleriacese where — as in the green group 

 Aphanochsetacese — ^both gamete cells are ciliate, but the egg 

 cell is much larger than the sperm cell. From this to the 

 condition seen in Fucacese where the egg cell is large and pas- 

 sive, while the sperm cell is minute and ciliate, transitions 

 can still be traced. 



The red seaweeds or Rhodophycese form the remaining 

 great algoid division. This, like the last, is so preponderat- 

 ingly marine that a fresh-water origin for it has seldom been 

 claimed. Thus Oltmanns (99, i; 537) says: "The Floridea? 

 are found scattered through all the seas of all zones, and one 

 can scarcely say whether they prefer any one region. Many 

 of them have become restricted to very saline regions, and 

 avoid seas that are less salt; others, however, inhabit these, 

 and many species of Florideae have even migrated into fresh 

 water. Batrachosperniiimy for example, lives in still as Avell 



