IOWA ACADEMY OF SCIENCE 
55 
Family II. 
Nostocaceae. 
KEY TO THE GENERA OF NOSTOCACEAE. 
A. Trichomes flexuose and contorted within a definite gelatinous investment 
1. Nostoc 
B. Trichomes more or less straight, free or forming a thin mucus stratum 
a. Heterocysts and spores intercalary 2. Anabaena 
b. Heterocysts terminal and spores always contiguous to them 
■k 3. Cylindrospermum 
1. Nostoc. 
KEY TO THE SPECIES. 
Thalli confluent, on soil or more frequently mosses N. muscorum 
Thalli discrete, periderm firm. 
Terrestrial. 
Thallus becoming irregular, tongue-shaped, etc N. commune 
Thallus remaining usually spherical or subglobose. . .N. sphaericum 
Aquatic. 
Trichomes densely intricate N. coeruleum 
Trichomes loosely implicate, radiating from the center. N. pruniform 
14. N. muscorum. Agardh. 
On the stem of mosses. 
Fayette. 1905. Fink. 
15. N. commune. Vaucher. 
A very common alga in the damp margins of marshy places, etc. 
Iowa City. 1880. Hobby. 
Ames. 1884. Bessey. 
Grinnell. Fink. 
Ames. 1904. Buchanan. 
Eagle Grove. 1904. Buchanan. 
16. N. sphaericum Vaucher. 
Iowa City. Hobby. 
Ames. Bessey. 
17. N. coeruleum Lyngbye. 
Ames. 1884. Bessey. 
18. N. pruniforme. Agardh. 
Fayette. Fink. Nodules often reaching the size of plum. 
Ames. Buchanan. In pool near Ontario. Very small. 
2. Anabaena. 
KEY TO THE SPECIES. 
Growing in roots of the Cycas A. cycadacearum 
Not in roots. 
Filaments straight, at least not spiral. Spores 7-13u broad 
A. flos-aquae 
