WISCONSIN PHYTOPLANKTON 41 



APHANOCAPSA Nageli 1849. 



Cells united to form spherical, ovoid, or amorphous colonies of micro- 

 scopic or macroscopic size. Colonies, hyaline, yellow, brown, or blue- 

 green in color. Cells spherical, equally distributed throughout the 

 colony but always some distance from one another; generally solitary, 

 rarely in clusters. Individual sheaths of cells confluent with the homo- 

 geneous, hyaline or colored, colonial envelope. Cell contents homogene- 

 ous ; usually pale to bright blue-green or grey in color. 



Reproduction by vegetative division of cells in three directions. 



KEY TO THE SPECIES. 



Cells growing within gelatinous envelope of other algae A. ENDOPHYTICA 



Cells forming free-floating or sessile colonies. 

 Cell contents grey to pale blue-green. 



Diameter of cells 3.5-4.5 M A. PULCHBA 



Diameter of cells less than 3 /*. 



Cell diameter not exceeding 1 /j. A. DELICATISSIMA. 



Cell diameter 1.5-2.5 M A. ELACHISTA 



Cell contents brightly colored, generally blue-green. 



Diameter of cells 3.5-5 n A. GREVILLEI 



Diameter of cells 5-6 /j. A. RIVULABIS 



APHANOCAPSA DELICATISSIMA W. & G. S. West. PI. 2, Fig. 7. 

 Jour. Linn. Soc. Bot. 40: 431, pi. 19, figs. 2-3. 1912. 



Colonies small, spherical, ovoid or irregular, free-floating. Colonial 

 envelope gelatinous, homogeneous, hyaline or ochraceous. Cells spheri- 

 cal, very small, more or less remote from one another. Cell contents 

 homogeneous, grey to pale blue-green. (Euplanktont). 



Cells .5-.T5 /A in diam. ; colonies 15-30 p. broad, 15-50 /* lonsr. 



Big Butternut (r), Chain (r), Little Butternut (ss), Loveless (ss), Mendota 

 (s), Poor Farm (r). 



The cells of this species are smaller than many bacteria and during 

 the first two year's study of the plankton flora these small colonies were 

 considered bacteria and not recorded so that the record for distribution 

 is far from complete. When the colonies are of any considerable size 

 the mass of cells has a decided blue-green color so that the organism 

 must be called a blue-green bacterium or a blue-green alga of bacterial 

 size. The latter view seems to be the more logical. It is very probable 

 that the bacteria have been derived from the blue-green algae and the 

 Wests' discovery of blue-green algae of bacterial size is very suggestive. 



