Algae in Some Colorado Soils. 
30 
Nodularia harveyana (Thwaites) Thuret. Plate I., figs. 11, 12. Soil 
samples 9, 13, 14, 15 , 16, 21 , 22 . Filaments long and straight, 6 mic. in 
diameter; sheaths thin, colorless, distinct; cells 5.2 mic. in diameter, 
1.5-3.9 mic. in length; heterocysts depressed, 5.2-5.4 mic. in diameter. 4.6- 
5.2 mic. in length; gonidia in long series between the heterocysts, 6.5-8 
mic. in diameter, 5.2-7 .8 mic. in length, yellowish-brown. 
Nodularia “A”. Plate IV., figs. 2 , 3. 4, 5. Soil sample 9. Filaments long 
and straight, 7-8.5 mic. in diameter; sheath colorless, distinct; cells disc¬ 
shaped 5.2-7.5 mic. in diameter, 1.5-2.5 mic. in length; heterocysts de¬ 
pressed, mostly occuring in pairs, yellowish-green, 7.1-7 .8 mic. in diameter. 
4.4-5. 6 mic. in length; gonidia spherical-depressed or spherical, brownish, 
7.2-8.3 mic. in diameter, 5.4-7.7 mic. in length; wall of gonidium smooth. 
Habitat: cultivated soil. 
Stigonema “A”. Plate II., fig. 1, and Plate III., figs. 1, 2. Soil sample 
16. Plant mass rust colored; filaments 20-46 mic. in diameter; sheath lamel- 
lose, constricted at joints, the outermost layers colorless, the inner ones 
yellowish or yellowish-brown, with a special envelop about each cell; 
trichomes single within each sheath; heterocysts terminal or intercalary, 
yellowish or orange-colored, 3 . 6-5 mic. in diameter. 5 mic. in length, oval 
or pear-shaped; cells spherical, oval, oblong or cylindrical, 4-5.2 mic. in 
diameter, 5.2-10 mic. in length, often attenuated; apical cell elongate, con¬ 
ical; gonidia (?) oval, the ends slightly attenuate, greenish brown, 5-5.7 
mic. in diameter, 7-10 mic. in length; wall of gonidium smooth. 
Stigonema sp. Here are grouped a number of polymorphic, transition 
forms of what appear to be one or more species of Stigonema. These forms 
are very abundant in the samples 'but the stages of development are not 
such as to permit one to come to any definite conclusions as to their 
identity. They are described and figured here as a record of algae found 
in cultivated soils. Soil samples 14, 22 . Plate II., fig. 3, and Plate IV., fig. 
9. Trichomes contorted, in sac-like gelatinous, colorless envelopes; cells 
irregular in shape 5.2-6.5 mic. in diameter; heterocysts terminal or inter- 
cala.ry, 5.2 mic. in diameter. Soil sample 22 . Plate II., fig. 2 , Probably 
a gonidial stage of the above. Sheath inflated at the ends; heterocysts 
terminal orintercalary;gonidia brownish. 6 .5-7 .8 mic. in diameter, 5.2 mic. 
in length; wall of gonidium smooth. Soil sample 21 . Plate II., fig. 4. Nu 
merous elongated colonies in which the trichomes are highly contorted; 
cells irregular in shape. 4. 6 - 6 .5 mic. in diameter. Soil samples 7, 18, 20 . 
Plate IIP, figs. 13, 14, 15, 16, 17, 18. Numerous spherical and oblong colo¬ 
nies of many sizes; cells 3.8-4 .2 mic. in diameter, irregular in shape. Soil 
samples 1 . 9. Plate II., fig. 4. Floating dark-brown crust; cells 5.2 mic. in 
diameter, irregular in shape; heterocysts 3.3 mic. in diameter, terminal or 
intercalary, some of them becoming thick-walled and granular. 
Rivularia “AT Plate II., figs. 5, 6 , 7, 8 , 9, 10. Soil samples 2 , 7, 18, 
20 . Numerous developmental stages are present in the above samples. 
Filaments 7-10 mic. in diameter tapering; sheaths colorless, close; basal 
cells 5.2-6 mic. in diameter, 2.6-5 mic. in length. 
Rivularia “B”. Plate II., figs. 11 . 12 . Soil sample 16. Filaments scat¬ 
tered in the sample; filaments branched; sheathes thin, ragged along the 
edges; basal cells 8-8.4 mic. in diameter, shorter than wide; heterocysts 
hemispherical, yellowish-green. 7.5 mic. in diameter. 
Unicellular green alga. Plate II., figs. 15, 16, 17. Soil samples 7, 19. 
Plant mass bright yellow green; both motile and resting bodies present; 
motile individuals elongate, 3.3-5.2 mic. in diameter. 5-11 mic. in length; 
flagella 2 in number at anterior end, slightly longer than body; resting 
bodies spherical, varying much in size, usually 10-12 mic. in diameter. 
Pleurococcus vulgaris Meneghini. Plate II., figs. 13. 14, soil capillarity 
tube. Unicellular, spherical forms, single or gathered into clusters. Cells 
