264 



PART III. THE CLASSIFICATION OF PLANTS. 



It is extremely probable that the life-history of these plants presents a 

 definite alternation of generations, the asexual form being the sporophyte. If 

 this be so, the affinity to the Bhodophycese \vhich is suggested by the similarity 

 of four spores developed in the sporangium of this group to the " tetraspores" of 



FIG. 189. Section of a female conceptacle, with surrounding tissue, of Fucus vesiculosus, 

 (x 50: after Thuret.) 



FIG. 190. Fucus vesiculosus. a Paraphysis, from male conceptacle, bearing antheridia ; 

 6 an oogonium with paraphyses ; c process of fertilisation, the extruded oosphere sur- 

 rounded by spermatozoids; d developing embryo, (x 160 : after Thuret.) 



