66 SEAWEEDS 



The Geographical Distribution of the Didyotacecc 

 is characteristic of temperate and tropical seas, but 

 reaches its maximum in the warmer waters of the 

 tropics. 



TILOPTERIDACE.E. 



General Characters. This small order is of uncer- 

 tain position, since the true character of the repro- 

 ductive organs has not yet been ascertained. These 

 are of two sorts : (1) bodies comparable with the 

 antheridia of the Cutleriacece ; (2) larger unilocular 

 bodies, presumptive oospheres. No process of fer- 

 tilisation has been observed, and the thai lus affords 

 from its morphological character no other clue than 

 the indication of strong agreement with the Ecto- 

 carpaccce. 



The Thallus in all three genera viz. Tilopteris, 

 Haplospora, and Scaphospora takes the form of tufts 

 of more or less branching filaments attached to the 

 substratum by root-hairs. In Tilopteris the branches 

 are opposite, and the primary branches bear short 

 secondary ones ; while in Haplospora and Scaphospora 

 the branches are alternate but irregular. The upper 

 portion of each filament always consists of a single 

 row of cells, while the lower consists of tiers of 

 several cells of equal length. Growth in length 

 takes place by intercalary division. The upper ends 

 of the branches are fine and hair-like, the cells 

 becoming longer, and containing little protoplasm 

 and few chromatophores. The cells contain each a 

 large central nucleus with nucleolus, surrounded by 



