EUPHYCOPHYTA 221 



one of the daughter nuclei acts as the fertilizing agent: this feature 

 has led to the suggestion that in the more advanced red algae the 

 contents of the antheridium are equivalent to a body which 

 formerly did divide. 



The carposporophyte is the generation that arises normally after 

 fertihzation and is parasitic upon the female plants. Cytologically 

 it is haploid in the primitive members and diploid in the remaining 

 members of the Rhodophyceae. Morphologically it comprises all 

 the structures arising from the fertihzed carpogonium, fusion cell 

 or cells and gonimoblasts. In more advanced forms it is often pro- 

 tected by a wall of gametophytic tissue. The carposporophyte and 

 the wall is termed the Cystocarp or Gonimocarp. The following 

 types of carposporophyte have been recognized: 



(i) Gonimoblasts arise from carpogonium without any prior 



fusion with a gametophyte cell. 

 (ii) Gonimoblasts arise from carpogonium after fusion with a 



gametophyte cell but without transfer of diploid nucleus, 

 (iii) Primary gonimoblasts transfer diploid nucleus to gameto- 

 phyte cells from which secondary gonimoblasts then arise, 

 (iv) Gonimoblasts arise from fusion cell, the diploid nucleus 

 having passed into a gametophyte cell. 

 {a) The gametophyte cell is a cell or cells of the carpogonial 



branch. 

 {h) The gametophyte cell is the support cell of the carpo- 

 gonial branch or a true auxihary cell cut off before or 

 after fertihzation. 



The tetraspores are formed either in superficial tetrasporangia 

 that terminate assimilatory filaments or short laterals, or in spor- 

 angia and short laterals that are sunk into the thallus, in which case 

 the fertile branch often becomes swollen and irregular in outhne. 

 In some cases, e.g. Plocamium, Dasya^ they are borne on special 

 lateral branches or stichidia. The division of the sporangia is 

 cruciate, zonate or tetrahedral. In some cases only two spores (bi- 

 spores) are formed, e.g. Corallinaceae, Ceramiaceae. Meiosis 

 normally occurs at the formation of the tetraspores, but when the 

 spores develop on sexual haploid plants, as sometimes happens, 

 there is no meiotic division and the products function as monospores. 

 In Agardhiella tenera apospory is sometimes found and again there 

 is no meiosis so that a succession of asexual plants can occur. In the 



