CHAPTER IV 



THE ALGAE : EUGLENOPHYCEAE, CHLOROPHYCEAE 



AND CYANOPHYCEAE 



The Phylum Thallophyta includes all those lowly plants which are devoid 

 of stem, root and leaves. In the Algae and Fungi the simpler forms consist 

 of a single cell or of a small colony of cells, while in the higher forms the 

 body, or thallus, consists either of a filament of cells joined end to end, or, 

 in the more complex types, of cellular tissue or of a system of filaments, some 

 running longitudinally and some transversely, the whole being embedded in 

 mucilage. The method of nutrition is holophytic. Chlorophyll is present 

 only in the Algae, and here its presence may be masked by other pigments. 

 Sexual reproduction occurs in most Thallophytes, but the process varies 

 enormously and shows very instructive stages of evolutionary development 

 towards increased complexity in the Algae and towards simplification and 

 reduction in the Fungi. Sexual reproduction is unknown in Euglenophyceae. 



The Bacteria are usually included in this phylum. They are either uni- 

 cellular or filamentous, they are devoid of chlorophyll, and reproduction is 

 by a simple process of fission. 



The phylum Thallophyta is subdivided into the following groups :— 



1. Algae {e.g.. Seaweeds). 



2. Fungi {e.g., Moulds, Mushrooms and Toadstools). 



3. Bacteria. 



4. Lichenes. 



ALGAE 



The Algae are aquatic or semi-aquatic Thallophyta in which all or most 

 of the cells of the thallus normally contain chlorophyll. The simpler types 

 are unicellular, but in the higher forms the thallus may become complicated 

 and of large size, with a considerable amount of cellular difl^erentiation. 

 Except in the Euglenophyceae reproduction is both sexual and asexual. In 

 the simpler members sexual reproduction consists of the fusion in pairs of 

 exactly similar, motile cells, called isogametes, while in the higher types 

 distinct sex organs are developed, which consist of antheridia, the male 

 organs, and oogonia, the female organs. The difi'erent gametes produced 

 in these sex organs may be shed and fuse externally (heterogamy), or the 

 female may be retained within the body of the plant and be fertilized by a 

 motile male gamete (oogamy). 



The Algae are classified according to the colour of the pigment present 

 in the cells. The following are the more important groups : — 



I. Euglenophyceae (Motile organisms, devoid of a cell wall, either 

 colourless or containing chlorophyll, often with various additional 

 pigments. 



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