Algae in Some Colorado Soils. 27 
failed to appear in these agar cultures and in many cases within 
2 or 3 weeks. In some instances subsequent reinoculations to agar 
were made from the Petri dishes. 
DESCRIPTIONS OF SOIL ALGAE. 
Hereinafter is included a brief description of each algal species 
found in the samples of soil examined. Although most of these 
species are described in the books on algae (1), it seemed desirable 
to give here complete descriptions and illustrations of all the spe¬ 
cies found in the soils examined. The reader will thus gain a bet¬ 
ter idea of the nature of the algal forms which, up to date, have 
been found in our soils. Some of the descriptions are taken from 
Tilden’s Minnesota Algae. Credit is due Miss Nellie Killgore- who 
made most of the drawings and both colored plates. 
It will be noted that with but two exceptions, all the species 
found in the soil samples belong to the blue-green algae (Cyan- 
ophyceae).. It will be recalled that the blue-greens include the 
simplest kinds of algae. They are characterized by simple asexual 
methods of reproduction and by the presence of a blue pigment, 
phycocyanin, in addition to a green pigment; the mixture results 
in a blue-green color. The plant body may be unicellular or multi¬ 
cellular. Unicellular forms may be single or grouped into colonies; 
multicellular species are mostly filamentous. It is worthy of note 
that the blue-grees found in the soils examined are all filamentous. 
Furthermore the largest proportion of them belong to the one fam¬ 
ily Nostocaceae. This family includes members usually possess¬ 
ing thick, gelatinous or mucous sheaths surrounding the trichomes, or 
rows of cells. Other families of blue-green, (Oscillatoriaceae, Stigon- 
emaceae and Rivulariaceae) represented in the soil, also have gelatin¬ 
ous coverings to the trichomes. I mention the fact that forms of 
algae which have gelatinous sheaths predominate here, because I be- 
keve that bacteria find in these sheaths a highly favorable nutritive 
medium. Ivossowitsch and Schloesing and Laurent observed that 
in their cultures which showed nitrogen fixation in great amounts, 
A ostoc, a blue-green alga with gelatinous sheaths, was the dominant 
form present. Again, the presence of this sheath probably accounts 
for the difficulty experienced in attempting to get such algae in pure 
cultures, free from their accompanying bacterial and fungal flora. 
The gelatinous coatings undoubtedly harbor a host of bacteria. Euro¬ 
pean investigators have experienced but comparatively little difficulty 
in getting the unicellular green algae in pure cultures. On the other 
hand, I find no recorded instance of pure cultures of such forms as 
A ostoc. Green algae do not as a rule have such thick coverings of 
gelatinous material as members of the blue-greens. 
We have succeeded in getting the green alga so abundant in Sam¬ 
ple 7 practically pure, while our efforts in this regard with blue-greens 
(1) The writer has made most use of Tilden’s Minnesota Algae and De Toni’s Sylloge 
Algarum, V ol. 5, the Myxophyceae. 
