PH^OPHYCE^E 93 



The Geographical Distribution is throughout all 

 seas, but the majority of the forms occur in the 

 North Atlantic. Chordaria, Mesoglcea, Castagnca, 

 Myriodadia, Petrospongiiim, Leathesia, Myriadis, and 

 Myrionema occur in British seas. 



ELACHISTACE^E 



General Characters. In its most simple form the 

 thallus consists of a mere tuft of branching filaments 

 with basipetal growth in length, but cushion-like 

 forms of thallus occur, composed of a basal layer 

 clothed with densely packed upright assimilative 

 filaments. The unilocular sporangia, mostly ovate 

 or pyriform in shape, arise as lateral out-growths from 

 the assimilative filaments, while the plurilocular spor- 

 angia (giving rise to gametes, which in one case at 

 least have been observed to conjugate) are produced 

 either in place of such filaments or by the differenti- 

 ation of a cell of one of them, or as an out-growth of 

 such a cell. Considerable diversity occurs within 

 the order in the development of the last-mentioned 

 bodies. 



The Thallus in no case attains a greater stature 

 than minute, filamentous tufts or patches, and in 

 most cases is epiphytic on larger Algae, especially 

 Fucaceai, inhabiting in some cases even the con- 

 ceptacles of these seaweeds. The rhizoids penetrate 

 the tissues of the host-plants, and some of the forms 

 send out runners, which traverse the tissues or creep 

 over the surface, giving rise to new plants by this 



