[Chap. XLVU THE ALGAE 635 



algal and coral reefs are found in the limestone rocks formed during the 

 Paleozoic Era. 



Fig. 291. Photographs of two coralline algae: A, Goniolithon; B, LithopJu/Uiiiu. 

 Courtesy of the N. Y. Botanical Garden. 



Asexual reproduction among the red algae occurs through fragmenta- 

 tion, or the formation of non-motile spores. Strange as it may seem, no 

 flagellate, motile cells of any kind are produced b\' the plants of this 

 group. Sexual reproduction is so unlike that known in any other algae 

 that a special terminology is necessary to describe it. The unique features 

 of these algae are of interest mainly as examples of peculiar outcomes of 

 eyolution. A few examples are cited below. 



Nemalion. When the tide is out, one may see the gelatinous strands 

 of the marine summer annual, Nemalion, attached to the rocks in the 

 midlittoral zone along coasts in temperate regions. It is a gelatinous 

 short-branched cylindrical plant with a reddish-brown color. Compared 

 with some other red algae its life history is simple, but it is more com- 

 plex than the life histories of other algae described in this chapter. It 

 will be described briefly. 



The female sex organs are apical cells of special short branches. The 

 apical cell (carpogonium), which contains the egg protoplast and re- 

 sembles an oogonium, terminates in a slender outgrowth (trichogyne). 

 There are also numerous small antheridia, each of which contains a non- 

 flagellate male cell (sperrrmtium) which is borne by water currents to 

 the trichogyne. After the male cell becomes attached to the trichogyne, 



