CHAPTER I 



^CLASSIFICATION 



In the older classifications the algae proper were simply divided into 

 four principal groups, Chlorophyceae or green algae, Cyano- 

 phyceae or blue-green algae, Phaeophyceae or brown algae and 

 Rhodophyceae or red algae. Now, however, that more is known 

 about the simpler organisms which used not to be regarded as 

 algae, it has been realized that there is no real justification for such 

 a distinction, and so the number of algal groups has been increased. 

 This is because it has become evident that the Flagellata and other 

 simple unicellular organisms must properly be regarded as algae, 

 even though of a very primitive kind. At present it is most con- 

 venient to divide the algae into ten classes, one of which, the 

 Nematophyceae, is perhaps somewhat speculative. One of the 

 principal bases of this classification is the diff"erence in pigmenta- 

 tion, and a recent study of this problem shows that it is fully 

 justified. 



(i) Cyanophyceae. The plants in this group show very little 

 evidence of differentiation, containing only a very simple form of 

 nuclear material, no proper chromatophore and no motile cells with 

 cilia or flagellae. The products of photosynthesis are sugars and 

 glycogen. The colour of the cells is commonly blue-green and 

 hence their name, the colour being due to the varying proportions 

 of the pigments phycocyanin and phycoerythrin. There is no 

 known sexual reproduction, propagation taking place by simple 

 division or else by vegetative means. 



(2) Chlorophyceae. This group used to comprise four great 

 subdivisions, the Isokontae (equal cilia), Stephanokontae (ringed 

 cilia), Akontae (no cilia) and Heterokontae (unlike cilia). It is now 

 more in keeping with our present knowledge to place the last 

 section into a separate class, and this is the procedure adopted in 

 most recent books. The plants of the Chlorophyceae exhibit a 

 great range of structure from simple unicells to plants with a 

 relatively complex organization, whilst the chromatophores also 

 vary considerably in shape and size. The final product of photo- 



CSA I 



