HIDDEN MARRIAGES 



557 



attached by suckers to rocks, shells, or other weeds, but have no true roots 

 absorption being performed 

 by the surface-cells of the 

 entire thallus. This assumes 

 a great variety of forms, 

 from the mere threads of 

 Batrachospermum and Ccd- 

 lithamnium, consisting of 

 a single row of cells, to the 

 broad leaf-like ribbons of 

 Delesseria with midrib and 

 nervures mimicking the 

 leaves of Phanerogams. In 

 Corallina (figs. 699, 703) the 

 thallas is so completely in- 

 vested with a layer of cal- 

 cium carbonate that its 

 vegetable nature is dis- 

 guised, and the plants were 

 long regarded as true corals. 

 There is no alternation of 

 generations, but there are 

 two modes of reproduction 

 sexual and asexual. The 

 asexual mode is by the 

 division of a mother-cell or 

 sporange, usually into four 

 (hence distinguishable by 

 the name of tetraspores). 

 which are set free by the 

 rupture of the sporange 

 walls. These tetraspores 

 are not ciliated, and have 

 no power of motion, but 

 float with the bea currents 

 until they come to rest and 

 vegetate on some suitable 

 surface. The sexual organs 

 are antherids and carpo- 

 gones. The contents of the 

 antherid, instead of being 

 broken up into aiithero- 

 zoids, go to form a more or less spherical spermatium. The carpogone 

 has a basal flask-shaped portion surmounted by a filamentous extension, the 



Photo 6y] [ - Ste P' 



FIG. 704. Jania rubens. 



fine thread-like stems grow in clusters from the stems of other Sea- 

 weeds, as here shown. The threads are all coated with lime. 



Tl 



