FLORIDE^E 



193 



tissue into epidermal, assi- 

 milating, and conducting 

 systems, still there are, in 

 the higher forms, cells which 

 are especially concerned 

 with assimilation, and which 

 may be either isodiame- 

 .trical. or elongated in either 

 direction. Such assimilat- 

 ing tracts are classed by 

 Wille under three heads, 

 ^viz. : (i) those which act 

 .also for purposes of con- 

 ducting ; (2) those which 

 are altogether distinct from 

 the conducting cells ; and 

 (3) those where, in addition 

 to an assimilating, there are 

 also primary and secondary 

 conducting cells. In some 

 species the 'frond' assumes 

 the appearance of a stalked 

 leaf, as in Hydrolapathum 

 (Rupr.) and Delesseria 

 (Grev.), often of the most 

 beautiful form, and present- 

 ing even a rudimentary 

 venation. The genera 

 Melobesia (Lmx.), Hilden- 

 brandtia, Cruoria, and some 

 others, consist of small 

 algae, mostly marine, with 

 crustaceous or gelatinous 

 thallus, growing flat on 

 stones or larger algae, often 

 of lichen-like appearance. 

 In their mode of growth 

 some Florideae display bi- 

 lateral symmetry, and the 

 branching may be either 

 monopodial or sympodial. 

 In Polysiphonia, Spyridia 



FIG. 170. Polysiphonia. opaca Zan. , with cystocarpxs ; 

 b, with tetrasporanges (natural size) ; c, branch with 

 tetrasporanges ; d, branch with cystocarp ( x 100). 

 (After Kiitzing.) 



