CERAMIALES 



237 



normal tetrasporic plants, but as the procarp bi^anch in this case 

 develops normally without meiosis the carpogonium is diploid. 

 Fusion of the nuclei in the carpogonium has been observed so that 

 the gonimoblast filaments must be tetraploid, but unfortunately 

 the fate of the carpospores is not known. In S. Snyderae the tetra- 

 sporangia are replaced by polysporangia which must be regarded as 

 homologous structures. The mother cells of each polysporangium 

 contain two to nine nuclei and they give rise to twelve, sixteen, 

 twenty, twenty-four or twenty-eight spores. 



Ceramiaceae: Plumaria {pluma, soft feather). Fig. 157. 



The filamentous thallus is much branched, the main axis, which 

 is monosiphonous throughout, being ecorticate near the apex but 



Fig. 157. Plumaria elegans. A, plant (xf). B, antheridial ramuli (xi8o). 

 C, paraspores (X213). D, tetrasporic ramuli (X126). (A, original; B, after 

 Drew; C, D, after Suneson.) 



corticate below. The antheridia are borne on special branches, 

 whilst the four-celled carpogonial branch develops from the sub- 

 terminal cell of an ordinary branch. In northern waters P. elegans 

 never bears sex organs and only plants with paraspores are to be 

 found, whilst in southern waters the sexual (« = 3i) and tetrasporic 

 plants {n = 62) are predominant. Recent investigation has shown 

 that in this species we are concerned with a triploid race (n = g2) ^^ 

 the northern waters which reproduces by means of paraspores. 

 There is apparently no relation between the triploid plants and the 



