ii6 PLANT LIFE. 



The sexual reproductive organs consist of antheridia and 

 oogonia, which are produced in cavities called conceptades. 

 The conceptades are situated near the circumference of the 

 thallus, are circular in section, and communicate with the 

 exterior by a narrow mouth or ostiole, and may be compared 

 to circular flasks immersed in the substance of the thallus, 

 and communicating with the surrounding water by a small 

 mouth. 



In some species, as Hitnanthalia lorea, the conceptades are 

 scattered over the entire surface of the receptacle ; but they 

 more frequently form crowded patches at the tips of the 

 branches, as in the genus Fucus ; in Sargassum they are 

 produced on special branches of the thallus. 



In some species the conceptades are exclusively male or 

 female, and in such cases the species are always dixcious, 

 that is, the male and female conceptades are borne by 

 distinct plants, as in Fucus vesiculosus ; in others, the same 

 conceptacle contains both antheridia and oogonia, as in 

 Fucus furcatus. 



In the dioecious species the male plants can be recog- 

 nized by the orange colour of their conceptades, the female 

 conceptades being dull in colour. 



The inner walls of the conceptades bear numerous fila- 

 mentous, jointed cells, some of which remain sterile, and in 

 some species project through the mouth of the conceptacle 

 into the water ; such barren filaments are known as para- 

 physes. In the male conceptades the filaments are usually 

 branched, and the antheridia are formed from lateral 

 ramifications of the branched filaments. Each antheridium 

 consists of a thin-walled oval cell, the protoplasm of which 

 breaks up into numerous — usually sixty-four — antherozoids. 

 These are very minute, pear-shaped ; contain a nucleus and 



