196 



ALG.'E 



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

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

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

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

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

 h)ph£e or paraphyses. In others again they are borne on metamorphosed 

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

 6cc. Only in the Porphyraceae are the tetraspores endowed with a slow 



Fig. 173. — Xitophyllui7i pu7ictatia)i Harv. a, piece of frond with tetrasporanges (natural size) ; b, piece 

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

 (After Kiitzing.) 



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

 in the Ulvaceae ; 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 ge7}wicE. 

 In ]Monospora (Sol.) stalked gemmae or prop agules 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). 



