154 THE ALGAE 



known. When this genus comes to be investigated it will probably 

 be found to have a life history similar to that of the other Meso- 

 gloiaceae. 



Corynophlaeaceae: Leathesia (after G. R. Leathes). Fig. 84 



The present genus provides an example of degeneration in the 

 cable type of construction. The young plant arises from a small, 

 creeping, rhizomatous portion and is composed of a packed mass of 



Fig. 84 Leathesia dijformis. A, plants on Furcellaria fastigiata. B, 

 [ transverse section to show thallus construction ( x 24). C, unilocular 



sporangia ( x 336). D, plurilocular sporangia ( x 336). (A, after 

 Oltmanns; B-D, after Newton.) 



radiating, dichotomously branched filaments which are sufficiendy 

 closely entwined to make the plant mass solid. From these medul- 

 lary filaments there arises a cortex of densely packed assimilatory 

 filaments from which occasional colourless hairs emerge. The 

 young plants are subspherical at first, but with increasing age the 

 central medullary filaments commence to disintegrate and as a 

 result the mature thallus becomes hollow and irregularly lobed. 

 Plurilocular and unilocular sporangia are known, the zoospores 

 from the ovoid unilocular sporangia germinating to disc-like 

 plantlets on which plurilocular gametangia ultimately appear. 

 These plantlets either give rise to other similar plandets or else to 

 the adult thallus once more. By analogy with other species the 



