236 



RHODOPHYCEAE 



cut off by a wall. It is from the large upper cell that the gonimo- 

 blast filaments arise and so the mature cystocarp is produced. 



The sessile tetrasporangia arise in acropetal succession as lateral 

 outgrowths of the vegetative cells of young branches. In C. hra- 

 chiatum mature tetrasporangia and antheridia have been found 

 on the same plant, whilst other plants have been reported that bear 



Fig. 156. Callithamnion. A-I, stages in development of carpospores after 

 fertilization. J, antheridia. K, the same enlarged. L, secondary spermatium. 

 M, young tetraspore. N, mature tetraspore. O, amoeboid processes. (A-I, after 

 Oltmanns; J-L, after Grubb; M, N, schematic after Mathias; O, after Phillips.) 



both tetrasporangia and cystocarps. In these cases the nuclei of the 

 carpospores were found to be haploid whilst those of the vegetative 

 cells were diploid, so that if fertilization occurred there must have 

 been two meiotic divisions, one before and one after fertilization. 

 If only one meiotic division occurs then it must be supposed that 

 the carpospores arose apogamously. Spermothamnion Turneri is 

 another plant in which sex organs have also been reported on 



