62 
IOWA ACADEMY OF SCIENCE 
KEY TO THE SPECIES. 
Chromatophores usually numerous, cell wall thin. 
Diameter of filaments 6-11 u T. bombycinum 
Diameter of filaments 3-6 u T. bombycinum tenue 
Chromatophores numerous, large, cell wall thicker, diameter of cell 11-16.5 u 
T. utriculosum 
51. T. bombycinum (Agardh) Derb. & Sol. 
Very common in stagnant water, and even slow flowing water and springs. 
Eagle Grove. Slough, margin of. Buchanan. 
Ames. Floating in spring. Buchanan. 
52. T. bombycinum tenue Hazen. 
Eagle Grove. Slough. Buchanan. 
Eagle Grove. In pond amid Lemna. Buchanan. 
53. T. utriculosum (Kutz) Hazen. 
Eagle Grove. In rain barrel by the side of railroad. 
Eagle Grove. Pond by the side of the railroad. 
Ames. In pond near Ontario. Buchanan. 
Family II. 
Botrydiaceae. 
1. Botrydium. 
5 h. B. granulatum (L.) Crev. 
Occurs abundantly on mud just drying up, such as that found on the 
banks of a stream that has overflowed. 
Ames. 1884. On damp earth in autumn, forming a green coating. Bessey. 
Universally distributed in the state. Fink. 
Ames. Common in muddy places. Buchanan. 
Class IV. 
CHLOROPHYCEAE. 
This is the group to which by far the larger part of the algae 
found in the state belong. It has normally no other color than the 
chlorophyll pigment, and may generally on that account be easily 
recognized. 
KEY TO THE ORDERS OF THE CHLOROPHYCEAE. 
1. Thallus filamentous or unicellular. 
A. Thallus coenocytic, unseptate. Chloroplasts numerous, without pyre- 
noids. Sexual reproduction heterogamous VII. Siphoneae 
B. Thallus not coenocytic. 
a. Small unicellular, multicellular or colonial algae. Cells uninucleate 
or coenocytic. Chloroplasts very variable in form, size and dispo- 
sition, with or without pyrenoids. Sexual reproduction isogamous 
or heterogamous. Mostly fresh water IX. Protococcales 
b. Not characterized as a. 
