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 seciuence 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 surround 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 inclusions, such as sulfur. The term includes all gliding, non-flagellated organisms regardless of whether they are obviously multicellular, with all cells excepting terminal ones of uniform size and with square ends, or apparently unicellular organisms in chains.
The term includes also the obviously multicellular peritrichously flagellated organisms in which division of the trichome normally results in separation 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 special 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 individual 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.
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