BLADDER WRACK 29 



tents. Immediately inward from these cells are several 

 layers of cells which are nearly as broad as long and which 

 have brown cell contents. Cells of a third type are branched, 

 have little or no color and are found in the middle of the 

 thallus. 



Reproduction. The reproductive tissues are contained in 

 the swollen ends of certain branches. In these swollen 

 branches numerous somewhat spherical cavities or concep- 

 tacles extend the epidermis to form blister-like elevations; 

 in the center of each is a small opening extending into the 

 cavity. In Fucus vesiculosus the microscopic male and 

 female organs occur on different plants. It is necessary, 

 therefore, to cut sections of the conceptacles in order to 

 study them. 



Female Conceptacles. From the epidermal cells lining the 

 conceptacle grow numerous female reproductive organs or 

 oogonia. The contents of each oogonium by repeated division 

 divide into eight oospheres or female gametes. These when 

 mature break the wall of the oogonium and are forced through 

 the opening of the conceptacle into the sea water, because 

 the multicellular hairs lining the cavity become converted 

 into mucilage and because the outer cells of the thallus 

 become partially dry and contract during periods of low tide. 



Male Conceptacles. The epidermal cells of the male con- 

 ceptacle develop into two types of multicellular uniseriate 

 hairs, namely, non-branched mucilage hairs and branched 

 reproductive hairs. The terminal cells of the latter hairs 

 develop into antheridia. Each antheridium by repeated cell 

 division forms "sixty-four biciliate male gametes which are 

 set free in the conceptacle and later forced into the sea water 

 by the conversion of the hairs into mucilage and the partial 

 drying of the plant. 



