HOW TO KNOW THE FRESH- WATER ALGAE 



4a (1) Cells containing chloroplasts (bodies with green pigment pre- 

 dominating), or chromatophores (bodies with colors other than green 



predominating) 5 



4b Cells without chloroplasts and chromatophores, with pigments in 

 solution and more or less evenly diffused throughout the entire 



protoplast Subdivision Myxophyceae 376 



5a Plant grass- or leaf-green to gray-green; photosynthetic product 

 starch (iodine test positive), or paramylum (iodine test negative), 

 or floridean starch in the freshwater red algae which are greenish 



or violet-green (iodine test negative) 6 



Note: Because some Chlorophyta, or essentially green algae are 

 often tinged with red or yellow (the green color sometimes masked 

 by the other color), and because normally violet-green Rhodophyta 

 often appear green to the observer, the reader should compare plants 

 beipg keyed with: 



No. 22a in the key, Haematococcus, a red unicellular, motile organism; 

 No. 60a in the key, Botiyococcus, colonial green alga in a brown, 



nearly opaque mucilage; 

 No. 119a in the key, Rhodochytrium, a red unicell in the tissues of higher 



plants. 

 No. 238a in the key, Trentepohlia, an orange-colored member of the 



Chlorophyta. 

 No. 239a in the key, Batrachospermum, a filamentous member of the 



Rhodophyta which is gray- or violet-green; 

 No. 256a in the key, Cephaleuros, a filamentous, semiparasitic and 



nearly colorless member of the Chlorophyta; 

 No. 265a in the key; Leptosira, a yellowish-green filamentous mem- 

 ber of the Chlorophyta; and 

 No. 304a in the key, Botrydium, a green, balloon-like vesicle, belong- 

 ing to the Chrysophyta. 



Also, see Trachelomonas, Fig. 5, identified by a brown shell which 

 incloses a green protoplast, and Dinobryon, Fig. 243, which has a color- 

 less, cone-shaped envelope (lorica) containing a protoplast which ap- 

 pears greenish. 



5b Plant not grass- or leaf-green (but see Botrydium, Fig. 214, which 

 is green but belongs to the Chrysophyta (yellow-green algae); color 

 light green, violet-green, yellowish or brown; iodine test for starch 



negative 283 



6a Plants swimming in the vegetative state, solitary or colonial. (Pre- 

 served specimens should be examined for 2 or more minute pro- 

 tuberances at the anterior end of the cell which locate the position 

 of the flagella (organs of locomotion) that may have been retracted 



or lost). Use 5% glycerine for mounts. See fig. 17 7 



6b Plants not motile in the vegetative state; (check to be sure cell is 

 not a swimming organism at rest; see Trachelomonas, Fig. 5 which 

 although motile, is commonly found as a non-motile, brown shell 

 (lorica) from which the swimming protoplast has escaped); solitary, 

 colonial or filamentous 35 



22 



