PROTOPHYTA 65 



are provided with flagella and there is a tendency to regard them 

 as gametes, but conclusive evidence of this is lacking.* 



Class Cryptophyceae 



The order Cryptomonadida of protozoa becomes the Class 

 Cryptophyceae of the botanists, and is made up for the most part 

 of marine forms varying in size from 30m- to 80^. These differ 

 from Chrysomonads in having a constant body form, in being 

 laterally compressed, and in having a more or less distinct fur- 

 row or gullet. Many forms are colorless, but in the group as a 

 whole, chromatophores of yellow, brown, blue, blue-green, and 

 green color may be present, the color being dependent upon the 

 proportions of the four pigments (see page 45). The colorless 

 forms are saprophytic, i.e., they obtain their nutriment by absorp- 

 tion of dissolved proteins and carbohydrates which are present 

 in the surrounding medium. Such forms are common, therefore, 

 in stagnant pools, and one type, Chilomonas, is easily found (Fig. 

 29, page 58). As with other groups, so here, we find forms in 

 which the motile stage is dominant, e.g., Cryptomonas, Chilo- 

 monas, Nephroselmis, and other forms in which the palmella 

 state dominates. Motionless unicellular individuals are also well 

 known, and these, like Chlorella among the Chlorococcales, may 

 become symbiotic with animal cells. The best known examples 

 of this association (symbiosis'*") are the "yellow cells" (Zooxan- 

 thelleae) of Radiolaria and Foraminifera (see pages 76-78). 



Class Dinophyceae (Peridiniales) 



By far the most interesting of the plant flagellates in respect 

 to variety and power of adaptation are the Peridiniales of the 

 botanists or the Dinoflagellida of the zoologists. Some types are 

 sure to be found in stagnant pools or in reservoirs, e.g., Ceratium 

 tripos or Ceratium hirundinella (Fig. 33), but the great ma- 

 jority of the group are marine and Noctiluca miliaris in large 

 part is responsible for phosphorescence in the sea. Although 



* For a general description of diatoms, consult West and Fritsch, British 

 Fresh-Water Algae, 1927 edition; or Engler, Naturlichen Pftamenfamilien, Vol. 

 II, 1928. For the determination of species, consult W. Smith, A Synopsis of the 

 British Diatomacca (1853-56), or V. Schonfeldt in Pascher's Susstvasserflora 

 Deutschland's, etc., Jena, 1913. For marine forms, consult Karsten, "Bacillario- 

 phyta" in Engler's Naturlichen Pflancenfamilien cited above. 



t See the Glossary of this book, page 123. 



