Algae in Some Colorado Soils. 
29 
olive or *black in color; sheaths cylindrical, more or less unequal in out¬ 
line, agglutinated, pointed and closed at the apex, or open and gradually 
disappearing, at times entirely diffluent; trichomes 3 . 5-7 mic. in diameter, 
not constricted at joints, many within the sheath, closely crowded, usually 
twisted into cords, the portion extending from the shealth straight; apex of 
trichome gradually tapering and capitate; outer membrane of apical cell 
thickened into a depressed conical calyptra; cells 3-7 mic. in length; trans¬ 
verse walls frequently granulated. 
Nostoc “A”. Plate IIP. figs. 3, 4. Soil samples 1 , 10 , 11 , 13, 21 . Plant 
mass gelatinous, irregularly expanded, at first bright blue-green, becoming 
light olive or pale pea-green; filaments mostly straight sometimes loosely 
entangled or rarely spirally rolled; sheaths colorless, indistinct, becoming 
confluent; trichomes 5.2-6.7 mic. in diameter; cells different in shape, 
usually short depressed-spherical or barrel-shaped, 3 . 9 - 6.2 mic. in length, 
at first bright blue-green becoming grayish-green, the granules large and 
conspicuous; heterocysts yellowish-green, spherical, spherical-depressed 
or a little longer than wide, 6-8.3 mic. in diameter. 6-8 mic. in length; gon¬ 
idia 6-8 mic. in diameter, 8-13 mic. in length, oval to oblong, separated, often 
irregularly disposed, grayish-green; wall of gonidium smooth, colorless. 
Ha'bitat: cultivated soil. 
A small form of the above species (Plate I., fig. 8 ) occurs in samples 
11 and 21 . Trichomes 3.6-4.7 mic. in diameter; heterocysts 4. 3 - 5.9 mic. in 
diameter; gonidia 5.2-6.7 mic. in diameter, 7.8-11 mic. in length. 
Nostoc “B”. Plate III., figs. 5, 6 , 7, 8 , 9. Soil samples 1 , 2 . 4, 6 , 
8 . 10 , 11 . 15, 16, 20 . Plant mass bluish-white becoming yellowish with age, 
shapeless; filaments 15-20 mic. in diameter, flexuous, entangled, pale blue- 
green; trichomes 3-4.5 mic. in diameter, single in each colorless sheath: 
cells 'barrel-shapel or cylindrical, 3-6.5 mic. in length; heterocysis globose 
to elongate, 3.5-5.5 mic. in diameter. 5-5.2 mic. in length; gonidia numerous, 
separate, spherical to oval, brownish, 4. 5 - 5 .5 mic. in diameter 5-6.5 mic. in 
length; walls smooth. Habitat: cultivated soil. 
Nostoc “C”. Plate III., figs. 10, 11. Soil sample 4. Plant mass gela¬ 
tinous-membranaceous, bright olive or dark colored; filaments flexuous, 
entangled; trichomes 3.6-4 mic. in diameter: cells depressed-spherical, bar¬ 
rel-shaped or ellipsodial, blue-green, 3.6-5.7 mic. in length; heterocysts sub- 
globose or oblong 5-5.2 mic. in diameter; gonidia oval, in long series, 
5.2-6.2 mic. in diameter, 7.8-9 mic. in length; wall of gonidium smooth, 
deep amber. Habitat: cultivated soil. 
Nostoc commune Vaucher. Plate I., fig. 13. Soil samples 1, 2. 5, 8. 
11 , 15, 16. Plant mass gelatinous, not assuming here any definite form; fila¬ 
ments flexuous, entangled; sheaths colorless or brownish; trichomes 4.5-6 
mic. in diameter; (In samples 1 and 2, the trichomes are smaller, measur¬ 
ing 4-5 mic. in diameter) cells depressed-spherical or barrel-shaped; heter¬ 
ocysts 5.7-7 mic. in diameter, somewhat spherical; gonidia unknown. 
Anabaena “A”. Plate IV., figs. 6, 7, 8. Soil samples 1. 2, 5, 10, 13, 
14, 18. Plant mass gelatinous, dark green; trichomes 2.8-4 mic. in diameter, 
straight or flexuous; cells barrel-shaped, 3.9-5.2 mic. in length; heterocysts 
spherical to ovoid, 4-5 mic. in diameter. 4.6-5.4 mic. in length; gonidia ovoid 
when young, becoming cylindrical, solitary or in series contiguous to het¬ 
erocysts, 5-6 mic. in diameter, 10-18 mic. in length; wall of gonidium 
smooth, colorless. Habitat: cultivated soil. 
Nodularia armorica Thuret. Plate I., figs. 9. 10. Soil sample 21. Fila¬ 
ments 10-11 mic. in diameter, entangled; sheaths thin; cells depressed, one- 
half as long as diameter; heterocysts compressed, somewhat larger than 
the cell; gonidia depressed-spherical, yellowish-brown, in series, 10-12 mic. 
in diameter, 9 mic. in length; end walls of gonidia transversely truncate, 
projected. 
