212 



THE ALG^E 



and bottom of small cavities, called conceptacles (Fig. 199, A), 

 which are developed in swollen tips of older branches termed 

 receptacles (Fig. 198, r). Some species of Fucus (as F. edentatus) 

 have both male and female organs in the same conceptacle, but 

 in other species they are formed in different conceptacles, and 

 even upon different plants, as in F. vesiculosus. The female organ 

 is a large cell, or oogonium (Fig. 199, B, C}, which in Fucus 

 develops eight eggs. The male organs, antheridia, are also single 

 cells (Fig. 199, D), but they are generally borne in dense clusters 

 upon branching stalks, and each produces more than a hundred 

 very small sperms with two cilia at the side 

 (Fig. 199, E). The eggs and sperms are 

 forced out of the conceptacles by the swell- 

 ing of mucilage that is developed within 

 the structure, aided by the contraction of 

 the tissue when the plants are exposed at 

 low tide to the drying action of the air. 



The eggs are fertilized in the sea water 

 outside of the conceptacles. The sperms 

 gather around an egg in great numbers 

 (Fig. 199, F), making it revolve, and finally 

 one enters. The male nucleus passes rap- 

 idly to the center of the egg and in a few 



minutes begins to fuse with the female 

 FIG. 200. Sargassum , , ., . . 



Filipendula nucleus. The striking differences m size 



Tipofpiantshowingieaf- and structure between the large egg and 

 like lateral branches, minute sperm make the sexual process of 

 hollow fl^a'ts^and the Fiicus one of the best illustrations of heter- 

 f ruiting branches, or ogamy in the plant kingdom. Such ferti- 

 lized eggs as are fortunate enough to find 

 favorable resting places begin to germinate within twenty-four 

 hours, and develop directly into young Fucus plants. 



238. Sargassum. Sargassum (Fig. 200) is one of the Fucales 

 that deserves special mention for the complexity of its plant 

 body, which bears three forms of lateral structures: (I) thin, 



