EUPHYCOPHYTA 



155 



dwarf plantlets with the plurilocular sporangia may be regarded as 

 haploid gametophytes. 



The brown, flattened, spongy adherent plants of Petrospongium 

 can be regarded as a still more reduced form of the spherical 

 cushion. 



Elachistaceae : Elachista (very small). Fig. 85 



Church (1920) regarded this genus as being exphcable morpho- 

 logically on the cable type of construction, although it must be 

 regarded as a degenerate type in which the true structure is only 

 seen in the sporeling. This possesses a horizontal portion from 



Fig. 85 Elachista fucicola. A, plants on Fucus vesiculosus ( x 0-36). 

 B, single plant in section showing penetrating base, crowded 

 sporangia, short paraphyses and long assimilators. C, unilocular 

 sporangia ( x 120). D, plurilocular sporangia at base of assimilation 

 thread ( x 220). (A-C, after Taylor; D, after Kylin.) 



which a number of erect filaments arise, so that in the early stage 

 it is comparable morphologically to Eudesme. In the older plant the 

 erect filaments have developed to form a cushion composed of 

 densely branched filaments matted together and only becoming 

 free at the surface. The mature thallus comprises three distinct 

 regions. In the dense central portion there is a mat of profusely 



