196 



ALG^ 



near the margin of the ' frond,' sometimes (Rhodymenia bifida, Ktz.) im- 

 bedded in the thallus, and then often grouped into sort (Nitophyllum, 

 Grev.) ; or, in the CoraUinaceae, enclosed in special conceptacles. In 

 other genera (Phyllophora, Grev., &c.) they are developed in nematheceSy 

 wart-like elevations of the surface, where they are accompanied by barren 

 hyphse or paraphyses. In others again they are borne on metamorphosed 

 pod-like branches known as sfichids, as in Dasya (Ag.), Plocamium (Lmx.), 

 &c. Only in the Porphyraceae are the tetraspores endowed with a slow 



Fig. 173. — KitophyllumpvnctatKtit'R^xv. a, piece of frond ...LLt_t ^ ^_„ ( L l„.ze) 



of the thallus with tetrasporanges ( x 100) ; r, section through frond showing cystocarp 

 (After Kutzing.) 



; b, piece 

 (x 100,. 



amoeboid motion. Zoospores are altogether unknown in the class, except 

 in the Ulvacese ; but other modes of non-sexual propagation occur in a 

 few cases. In some genera of Ceramiacese special organs occur, known 

 as seirospores. Melobesia is characterised by the production oi gemmce. 

 In Monospora (Sol.) stalked gemmae or propaguks are produced at the 

 forks of the branchlets, and readily become detached, apparently repla- 

 cing the sexual organs, which are unknown in the genus. Lemanea 

 (Bory) increases by budding. In Hydrolapathum peculiar bud-like 

 prolifications are produced on the stem (see fig. 171). 



