EUPHYCOPHYTA 219 



are aggregated and true auxiliary cells are lacking, the adjacent 

 cells being only nutritive. Reduction division is delayed so that 

 the plants are morphologically triphasic and cytologically di- 

 phasic. The tetrasporangia are cruciate, more rarely tetrahedral. 



(3) Cryptonemiales : 



Both types of thallus construction. The carpogonia are borne 

 on special accessory branches and may be aggregated into sori, 

 nemathecia or in conceptacles. The auxiliary cell is borne on 

 separate accessory branches before fertilization and is actively 

 concerned in the post-fertiHzation processes. The tetraspor- 

 angia are cruciate or zonate. 



(4) Gigartinales : 



Both types of thallus construction. The support cell or a normal 

 intercalary cell of the mother plant is set aside as an auxiliary 

 cell before fertilization. The tetrasporangia are cruciate or 

 zonate. 



(5) Rhodymeniales : 



Central filament type of construction only. The small auxiliary 

 cells are derived from a branch formed from the support cell. 

 They are cut off before fertilization but only develop after that 

 process has taken place. The tetrasporangia are cruciate or 

 tetrahedral. 



(6) Ceramiales: 



Only the central filament type of construction. The auxiliary 

 cell or cells are cut off from the support cell or from an homo- 

 logous pericentral cell after fertiUzation and as a direct conse- 

 quence of the process. The tetraspores are usually arranged in a 

 tetrahedral fashion, more rarely in a cruciate manner. 



Some authors consider that a further two orders should be 

 recognized, the Sphaerococcales and Nemastomales, and there is 

 some evidence in support of this procedure. However, in this 

 volimie the genera of these two orders are retained in the existing 

 orders (above) to which they have belonged in the past. 



The antheridial plants, which are often paler in colour and more 

 gelatinous, were first mentioned in a letter to Linnaeus in 1767. 



