A COMPREHENSIVE KEY TO THE 

 GENERA OF THE MANUAL 



Use of the key 



First, determine the characters of the organism and then consult the key, 

 always commencing from the beginning. The key poses a series of questions 

 which can be answered in the affirmative or negative. Numbers on the right hand 

 side of the key indicate the next number on the left to be consulted. The se- 

 ciuence should be followed until the right hand number is replaced by a generic 

 name. Keys to the particular genus in the Manual should then be consulted 

 for species identification. 



1. Organisms green, blue-green or yellowish green, brown or red, containing chlorophyll 



"a" either in well-defined chloroplasts or in the cytoplasm Algae p. 30 



Organisms colorless; if pigmented, green pigments do not have the characteristics of 

 chlorophyll "a" 2 



2. Diameter or width of cells exceeds 2.0 microns; proceed to Section A p. 991 



Diameter or width does not exceed 2.0 microns; proceed to Section B p. 996 



Note: (1) In assessing diameter or width, measurement must be made of the 

 cells themselves and not of any capsular structures or sheaths which may sur- 

 round them. In Section A some cells have widths up to 100 microns and are 

 clearly visible to the naked eye. 



(2) To avoid confusion the following terms have the following meanings 

 throughout the key: 



Trichome: A uniseriate multicellular organism in which the multicellular 

 character is clearly visible without staining after removal of any cell inclu- 

 sions, such as sulfur. The term includes all gliding, non-flagellated organisms 

 regardless of whether they are obviously multicellular, with all cells except- 

 ing terminal ones of uniform size and with square ends, or apparently unicel- 

 lular organisms in chains. 



The term includes also the obviously multicellular peritrichously flagel- 

 lated organisms in which division of the trichome normally results in separa- 

 tion of obviously multicellular elements. The latter may, however, separate into 

 single discoid elements which grow out into multicellular forms. 



The term does not include the peritrichously flagellated cells which form 

 chains in which the individual cells do not appear multicellular without spe- 

 cial staining procedures. 



The presence or absence of a sheath should not be taken into consideration. 



Chain of cells: Organisms which characteristically divide in one plane only 

 and remain attached to each other by a continuity of the cell wall. The indi- 

 vidual cells do not appear multicellular without special staining. They are 

 either non-motile,or, if motile, possess flagella. The presence or absence of a 

 sheath should not be taken into consideration. 



Filament: An elongated rod which shows no evidence of multicellularity 

 without special staining. 



990 



