314 THE ALGAE 



Haplont: A sexual haploid plant with only the zygote diploid 

 ( Volvox). 



Diplont: A sexual diploid plant in which only the gametes are 

 haploid, e.g. Codium. 



Haplohiont: A plant possessing cytologically only one kind of in- 

 dividual in the life cycle : this may be either a haplont 

 or a diplont. 



Diplohiont: A plant possessing cytologically two kinds of indivi- 

 duals in the life cycle, and hence an alternation of 

 generations. 



These terms have been further elaborated by Feldmann as 

 follows : 



Types of cy tological cycles Morphological cycles 



1 . Reduction division at first division of monogenetic or 



zygote DIGENETIC 



HAPLOPHASic ( = haploid haplobiont) 



2. Reduction division at gametogenesis monogenetic 

 DiPLOPHASic ( = diploid haplobiont) 



3. Reduction division at spore formation, digenetic 



DIPLOHAPLOPHASIC ( = diplobiont) TRIGENETIC (tWO SporO- 



phyte generations — 

 e.g. carposporophyte 

 and tetrasporophyte) 



Representatives from the different algal groups in these cyto- 

 logical and morphological cycles are shown in Table 5, where the 

 digenetic forms are subdivided into those with alternation of like 

 generations (isomorphic) and those with unhke (heteromorphic). 

 Most Nemalionales are digenetic in so far that reduction division 

 occurs at zygote germination giving rise then to a parasitic haploid 

 carposporophyte. The Protoflorideae are digenetic in that some of 

 them possess an independent prostrate generation (Conchocelis 

 phase of Porphyr a). 



The primitive members of the Phaeophyceae (Ectocarpales) 

 known today already possess a form of thallus that is only seen in 

 advanced types of the Chlorophyceae, i.e. branched heterotrichous 

 filaments, with alternation of isomorphic generations. The actual 

 source of origin of the Phaeophyceae therefore presents some con- 



