RHODOPHYCEAE 213 



the other algal groups. The carpogonium with its trichogyne is borne 

 on a special branch {procarp) consisting of a varying number of 

 cells, whilst the typical auxiliary cell, into which the fertilized 

 carpogonial nucleus generally passes, is often associated with this 

 branch, or else forms a part of it. The fertilized zygote commonly 

 gives rise first to a peculiar diploid generation, the carposporophyte, 

 w^hich consists of a series of filaments that cut off asexual bodies 

 or carpospores from their apices. These spores on germination usually 

 give rise to the asexual or tetrasporic plant which reproduces by means 

 of tetraspores that are formed in sporangia borne externally or else 

 sunk into the thallus (cf. fig. 155, F). A common feature in this 

 group that further emphasizes their uniformity is a tendency for the 

 2x number of chromosomes to be 40. The Rhodophyceae may be 

 regarded as the classical example of plants in which meiosis occurs at 

 different phases in the life cycle, for it may either occur immediately 

 after fertilization or else at some subsequent period. In the former 

 case the plants are said to be haplohionts as there is only one kind 

 of individual or biont, but the individual sexual haploid plants are 

 termed haplonts. If meiosis is delayed we get an asexual generation 

 alternating with the sexual and so there are two kinds of indi- 

 viduals or bionts: this type is therefore known as diplobiontic. It 

 may be pointed out here that other usages of these terms have been 

 employed, but the above definitions are those propounded by 

 Svedelius (1931) who coined the terms, and therefore they are the 

 correct way in which they really should be employed. The 

 classification of the Rhodophyceae is based primarily on the 

 structure of the female reproductive apparatus. After the Proto- 

 florideae, which lack pit connexions, have been segregated, the 

 remainder of the red algae, or Eu-florideae, are classified as 

 follows : 



(i) Nemalionales and Gelidiales. 



These are regarded as primitive orders which have become more 

 or less stabilized. In some genera there are no true auxiliary cells, 

 whilst in others the auxiliary cells are purely nutritive, but never- 

 theless the beginnings of an evolutionary series can be seen in the 

 following features : 



{a) The development of the hypogenous cells of the carpogonial 

 branch to form storage organs. 



