28 
Colorado Experiment Station. 
are unsuccessful. We hope, however, to overcome the difficulties and 
obtain absolutely pure cultures of the most dominant blue-greens oc¬ 
curring in our soils. With such pure cultures we will be in a position 
to test their supposed nitrogen fixing power, and their role in the soil. 
A number of the species appear to be undescribed. Although it 
has been possible to follow these for some months with considerate 
care and satisfaction through to spore production and growing both 
in flasks on sterile ground quartz and in i% aqueous agar, these will, 
for the present, be designated by letters until further study of them is 
made. It has been impossible to identify certain other forms on ac¬ 
count of their immaturity. For example Stigonema and Riviilaria 
specimens were in developmental stages. 
It was anticipated that the systematic study of algae occurring on 
and in the surface layers of soil would be attended with diff'culty. 
This is largely due to the fact that no previous studies of soil algae 
have, to our knowledge, been made; furthermore, the descriptions of 
many species are totally inadequate and undifferentiating. It is need¬ 
less to say that a systematic study of these soil organisms is highly 
essential. It is our purpose to continue the systematic study of the 
algal flora of Colorado soils as well as its relation to nitrogen fix¬ 
ation. 
/ 
Oscillatoria formosa Bory. Plate I., fig. 1. Soil capillarity tube. Plant 
mass dark blue green; trichomes straight, elongate, usually slightly con¬ 
stricted at joints; apex of trichome somewhat obtuse and briefly tapering 
or rotund, hooked, not capitate; calyptra none; cells 2.5-5 mic. long; 
transverse walls finely granulate; cell contents bright blue-green. 
Phormidium inundatum Kuetzing. Plate I., fig. 2. Soil samples 9, 10, and 
soil capillarity tube. Filaments somewhat straight, fragile; scattered in the 
flask cultures among other algae; sheaths thin; trichomes 3-5 mic. in 
diameter, straight or curved, not constricted at joints; apex of trichome 
straight, briefly tapering, not capitate; apical cell obtuse conical; calyptra 
none; cells 4-8 mic. in length; transverse walls covered with protoplasmic 
granules. 
Phormidium subuliforme Gomont. Plate I., fig. 3. Soil sample 10. Fila¬ 
ments scattered throughout other algae; trichomes 2-2.8 mic. in diameter, 
straight^ constricted at jointsf apex of trichome gradually tapering, bent 
or twisted, not capitate; apical cell more or less acute-conical; calyptra 
none; cells 6-8 mic. in length; transverse walls indistinct; cell contents 
homogeneous or coarsely granular, blue-green. 
Phormidium tenue (Meneghini) Gomont. Plate I., fig. 4. Soil samples 
4, 10. 11, 16, 18 and soil capillarity tube. Plant mass thin, membraneous, 
expanded, pale blue-green; filaments elongate, straight, entangled; sheaths 
thin; trichomes 1-2 mic. in diameter, straight, somewhat constricted at 
joints; apex of trichome at first straight becoming tapering and bent; 
cells 2.5-5 mic. in length; transverse walls usually indistinct. 
Phormidium valderianum (Delponte) Gomont. Plate I., fig. 5. Soil 
samples 13, 15. Filaments flexuose, densely entangled, here scattered 
throughout other algae; trichomes 2 - 2.5 mic. m diameter, straight not con¬ 
stricted at joints, apex of trichome not tapering; apical cell rotund; caly¬ 
ptra none; cells 3.3-6.7 mic. in length; transverse walls marked by two or 
four protoplasmic granules; cell contents blue-green. 
Microcoleus vaginatus (Vaucher) Gomont. Plate I., figs. 6, 7. Soil 
capillarity tube. Filaments forming entangled and twisted threads, dark 
