228 SEAWEEDS 



place with the auxiliary cell and the nuclei of both 

 unite. 



The formation of the wall of the cystocarp begins 

 when the carpogonium has been fertilised and the 

 auxiliary cell is recognisable. Branched filaments 

 arise from the thallus-cells in the immediate vicinity 

 of the one which bears the carpogonial branch, and 

 their apices meet over the auxiliary cell and the 

 whole body assumes a globular form. It is note- 

 worthy that these filaments have no pore connections 

 with the carpogonial or the auxiliary cell. They 

 develop into the cystocarp wall, which at first so 

 confines and presses against the swelling carpogonial 

 and auxiliary cell that the contents of the wall-cells 

 next adjoining die off and their membranes swell 

 up. At about this stage the auxiliary cell, after 

 union with the carpogonial cell, fuses with its parent 

 cell, and the whole .united cylindrical body extends 

 a kind of foot into the thallus beneath it. It may 

 now for convenience sake be called the central cell. 

 From its apical region there are now produced a 

 number of marginal (gonimoblast) cells which have 

 pore-connections with the central cell, and each of 

 these gives rise to a carpospore. The central cell pro- 

 ceeds to unite below with cells of the thallus 

 adjoining it, while it bears more gonimoblast cells 

 on its upper and middle portions. In the ripe fruit 

 only the outermost layer of cells of the wall remains, 

 and these swell up and yield at the apex, permitting 

 the egress of the carpospores. 



Minor differences occur in the allied genera Cham- 

 pia and Lomentaria. Among these it may be noted 



