PH^OSPOREJl 251 



three rays diverging above, with a hair springing from the centre of the 

 rays. They become detached like the basidiospores of Fungi, and are 

 constantly being formed afresh. 



Literature. 



Geyler— Pringsheim's Jahrb. wiss. Bot., 1866, p. 479. 



Janczewski— Mem. Soc. Sc. Nat. Cherbourg, xvi., 1872, p. 337 ; and Ann. Sc. Nat.> 



1873, p. 253. 

 Magnus— Zur Morphologic der Sphacelarieen, 1873. 

 Pringsheim— Abhandl. Berlin Akad., 1873, p. 137. 

 Rischawi— Algol. Untersuch., i., 1874 (Just's Jahrb. , 1874, p. 13). 

 Wollny — Hedwigia, 1880, p. 65. 



The Ralfsiace^ (Ralfsia, Berk., Lithoderma, Aresch., &c.) are small 



seaweeds (with the exception of two species of Lithoderma which grow 



in fresh running water) with crustaceous thallus, attached to stones, 



rocks, or the shells of molluscs and Crustacea, composed of a pseudo- 



" _^ * 



I 





Fig. 225. — Lithoderma faiiscens Aresch. tf, vertical secticn of portion of thallus with 

 unilocular zoosporanges ; b, with multilocular zoosporanges ( x 320). (After Hauck.) 



parenchymatous tissue of vertical rows of cells. They have both kinds 

 of sporange, collected into wart-like groups or sori on the surface of the 

 thallus, but nothing is known with regard to the function of the swarm- 

 spores. 



The small order of Cutleriace^, comprising the genera Cutleria 

 (Grev.), Zanardinia (Nard.), and Aglaozonia (Zan.), consists of a small 

 number of seaweeds, nearly all natives of warmer seas, although others 

 from colder climates have been erroneously included in it. The thallus 

 is coriaceous or membranaceous, flat, and either erect (Cutleria), or 

 prostrate (Zanardinia), with the peculiarity that the marginal filaments 

 are dissociated in their growth from the rest of the ' frond.' A true 

 sexual mode of reproduction has been observed by Reinke in Zanardinia, 

 and by Falkenberg and Janczewski in Cutleria. The former genus is 

 monoecious, the latter dioecious. The oogones and antherids are both 

 collected into sori, the former very dark brown, the latter orange-coloured. 



