144 



BOTANY. 



entiation of portions of the plant-body into general repro- 

 auctive organs, analogous to the floral branches of higher 

 plants. The sexual organs are developed upon modified 

 branches, which drfiEer more or less in 

 shape and appearance from the ordi- 

 nary ones. 



297. In Rockweed (Fucus) the sex- 

 ual organs are found in the thickened 

 ends of the lateral branches {A, Fig. 

 72). They occur on the walls of 

 cavities termed conceptacles, which 

 are spherical, with a small opening at 

 the top {B, Fig. 72). The concepta- 

 cles are at first portions of the general 

 surface, and afterward become de- 

 pressed and walled in by the over- 

 growth of the surrounding tissues; 

 they are thus in reality portions of the 

 general surface. 



298. 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, which are them- 

 selves, as Sachs has pointed out, 

 modified hairs. The antherids are 



produced as lateral branches of hairs {A, Fig. 73); each 

 antherid is a thin-walled cell, whose protoplasm breaks up 

 into a large number of biciliate antherozoids, which escape 

 by the rupture of the surrounding wall {S). Before rup- 

 turing, however, the antherids detach themselves and float 

 in the water with their contained antherozoids. 



Fia. 71. Part of a plant o£ 

 knotted Eockweed (Asoo- 

 phylliim nodosum), show- 

 ing the air-bladders. Nat- 

 ural size. 



