36 
Colorado Experiment Station. 
The algae occur in a variety of soil types, for example, sandy 
loam, clay loam, heavy clay, hard, gravelly clay, heavy adobe and river 
bottom silt. 
The most prevalent species of algae are Phormidium tcnue, 
Nostoc spp., Anabaena sp., Nodularia harveyana and Stigonema sp. 
In many Colorado soils, algae may be considered as an important 
source of energy for Azotobactcr. 
EXPLANATION OF PLATES. 
Fig. 
1 . 
Fig. 
2. 
Fig. 
3. 
Fig. 
4. 
Fig. 
5. 
Fig. 
6. 
Fig. 
7. 
Fig. 
8. 
Fig. 
9. 
Fig. 
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Fig. 
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Fig. 
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Fig. 
13. 
PLATE I. 
Oscillatoria formosa. 
Phormidium inundatum. 
Phormidium subuliforme. 
Phormidium tenue. 
Phormidium valderianum. 
Microcoleus vaginatus, filaments within sheath. 
Microcoleus vaginatus, single fliament. 
Nostoc “A”, small form 
Nodularia armorica. 
Nodularia armorica, gonidia. 
Nodularia harveyana. 
Nodularia harveyana, gonidia. 
Nostoc commune. 
PLATE II. 
Fig. 1. Stigonema “A”, gonidia (?). 
Figs. 2, 3, 4. Stigonema sp 
Figs. 5, 6, 7. Rivularia “A”. 
Figs. 8, 9, 10.. Rivularia “A”, young forms. 
Figs. 11, 12. Rivularia *‘Byoung forms. 
Figs. 13, 14. Pleurococcus vulgaris. 
Fig. 15. Unicellular green agla, resting form, the contents dividing up into 
motile bodies. 
Fig. 16. LTnicellular green alga, resting stage. 
Fig. 17. Unicellular green alga, motile body. 
Fig. 18. Navicula, a diatom. 
PLATE III. 
Figs. 1, 2. Stigonema “A”. 
Fig. 3. Nostoc “A”, vegetative filament. 
Fig. 4. Nostoc “A”, gonidia. 
Fig. 5. Anabaena “A”, vegetative filament. 
Fig. 6. Anabaena “A”, filament producing gonidia. 
Figs. 7, 8, 9. Anabaena “A”, germinating gonidia. 
Fig. 10. Nostoc “C”, vegetative filament. 
Fig. 11. Nostoc “C , gonidia. 
Figs. 12, 13, 14, 15, 16, 17, 18. Stigonema sp., developmental forms. 
PLATE IV. 
Fig. 1. Soil capillarity tube a 10-inch section from the 7th to 17th inch. 
Fig. 2. Nodularia “A”, filament producing gonidia. 
Fig. ^ 3. Nodularia “A”, vegetative filament. 
Figs. 4, 5. Nodularia “A”, germinating gonidia. 
Fig. 6. Nostoc “B”, gonidia. 
Fig. 7. Nostoc “B”, germinating gonidium. 
Fig. 8. Nostoc “B”, vegetative cells and gonidia. 
Fig. 9. Nostoc “B”, vegetative cells and gonidia. 
Fig. 10. Flask culture cf soil sample No. 1. 
