202 PHYLUM V. PHAEOPHYCEAE 



310. In common Rockweeds (Fucus) of the seashore 

 the sexual organs are found in the thickened ends of the 

 lateral branches. They occur on the walls of cavities 

 (conceptacles) , which are spherical, with a small opening 

 at the top. The conceptacles are at first portions of the 

 general surface, and afterward become depressed and 

 walled in by the overgrowth of the surrounding tissues; 

 they are thus in reality portions of the general surface. 



311. The walls of the conceptacles are clothed with 

 pointed hairs, which in some species project through the 

 opening, and among these are found the sexual organs. 

 The antherids are produced as lateral branches of hairs; 

 each antherid is a thin-walled structure containing a 

 large number of biciliated sperms, which escape by the 

 rupture of the surrounding wall. Before rupturing, 

 however, the antherids detach themselves and float in the 

 water with their contained sperms. 



312. The oogone is a globular or ovoid short-stalked 

 body containing eight eggs. These escape from the 

 oogone and float out through the opening of the concep- 

 tacle, into the open water. The sperms, which are lib- 

 erated at about the same time, gather around the 

 inactive eggs in great numbers, and by the vigor of 

 their movements sometimes actually give them a rotary 

 motion. Fertilization results from the union of one of 

 these sperms with the egg, the zygote thus produced 

 secreting a wall of cellulose about itself. 



313. In germination the zygote lengthens and under- 

 goes division into numerous cells; at the same time it 

 elongates below into root-like processes, which serve to 

 hold fast the new plant. 



314. In the nearly related Gulfweeds (Sargassum) the 

 plant body is composed of a distinct stem, rooted below, 

 and bearing leaves above. The stem bears also many 



