THE OniGIN OF LIFE 



Figure 32. Representatre Algae of Several Phyla. A, OsciUatoria, a blue-green 

 alga; B, Syniira, a golden-brown alga; C, Fiicus, a brown alga; D, Batrachospermum, 

 a red alga, showing growth habit and details of one whorl; E, Euglena; F, Amphidinium, 

 a dinofiagellate. {A, C, and D redrawn from Weatherwax; B and D redrawn from 

 Fuller and Tippo; and F redrawn from Kofoid and Swezy. ) 



Protozoa, and the viewpoint that the Eumycophyta may be of Protozoan 

 origin is currently gaining much support. 



The remainder of the old phylum Thallophyta comprises seven phyla, 

 the various types of algae (Figure 32), ranging in complexity from the 

 exti-emely simple, unicellular blue-green algae to the green algae of large 

 size and complexity only a little less than that of the vascular plants. Most 

 of these phyla are of uncertain origin and have given rise to no further 

 groups, hence they need not be discussed here in detail, even though some 

 of them have attained a considerable degree of specialization. These are 

 the phylum Chrysophyta, including yellow-green algae, golden-brown al- 

 gae, and diatoms; the phylum Pyrrophyta, including cryptomonads and 

 dinoflagellates; the phylum Phaeophyta or brown algae which Dillon and 

 Hutner believe to he of especial importance for the origin of animals; 

 and the phylum Rhodophyta or red algae. Three more phyla of algae (this 

 term means seaweeds, and is based upon the larger members of this di- 

 verse group) are of more especial interest for the present discussion: these 

 are the Cyanophyta or blue-green algae; the Euglenophyta, including 

 Euglena and its allies; and the Chlorophyta or green algae. 



The Cyanophyta. The Cyanophyta or blue-green algae are undoubt- 

 edly the most primitive of all green plants. The individual plant is always 

 unicellular, but these may form colonies of moderate size. There is, how- 

 ever, no differentiation within such colonies. Cytoplasm is much more 

 abundant than in the bacterial cell, but there is still no morphological 

 separation of nucleus and cytoplasm. No evidence of sexual processes has 

 ever been observed in the blue-green algae, reproduction apparently oc- 

 curring exclusively by simple fission. In all other green plants, the chloro- 



101 



