CERAMIALES . 235 



rise to a four-celled carpogonial branch. In the original branch of 

 three cells the first cell gives rise to a protective branch after fruiting 

 has occurred, whilst the third cell remains sterile throughout. The 

 tetraspores, which are borne in whorls, are partly covered by in- 

 volucral cells. At tetraspore formation, after a small support cell 

 has been cut off from an ordinary vegetative cell it proceeds to cut 

 off several side cells, each of which functions as a tetrasporangium. 

 Finally the support cell cuts off two sterile cells at its apex, the 

 distal one enlarging to become a protective cell for the whorl of 

 tetraspores. 



*Ceramiaceae: Callithamnion {calli^ beauty; thamnion^ small 

 bush). Fig. 156. 



This is a genus of very beautiful and delicate plants that possess 

 filamentous branched fronds which are either monosiphonous or 

 else corticated at the base, the cortication being formed by rhizoidal 

 filaments. The cells of the vegetative thallus are multinucleate, 

 and in C. hyssoides there are protoplasmic pseudopodia projecting 

 internally from the ends of the cells, and although these strands are 

 apparently capable of some movement their function is obscure. 



The antheridia, which form hemispherical or ellipsoidal tufts on 

 the branches, arise as lateral appendages, the first cell to be cut off 

 being the stalk cell. This stalk cell gives rise to a group of secondary 

 cells which later on divide to form branches composed of two to 

 three cells, each terminating in an antheridial mother cell. In this 

 genus there may be two or even three crops of antheridia arising 

 successively in the same place, each mother cell producing about 

 three antheridia in every crop. The cystocarps, which are usually 

 present in pairs and enclosed in a gelatinous envelope, arise as 

 follows. Two cells are cut off from a cell in the middle of a branch 

 and these function as the auxiliary mother cells. From one of them 

 the four-celled carpogonial branch is produced, whilst after fertiliza- 

 tion both auxiliary mother cells divide and cut off a small basal 

 cell. The fertilized carpogonium also divides into two large cells, 

 each of which cuts off a small sporogenous cell that fuses with the 

 adjacent auxiliary cell. As a result of this fusion each auxiliary cell 

 can receive a diploid nucleus which soon after its entry divides into 

 two ; one daughter nucleus passes to the apex of the auxiliary cell, 

 whilst the other, together with the nucleus of the auxiliary cell, is 



