122 
EDGAR NELSON TRANSEAU 
The second source of information is the study of algae in the field. 
Comere studied the algae of the vicinity of Toulouse, France. In 
addition to a classification of the habitat groups of algae, he classified 
the local species into seasonal groups on the basis of their times of 
reproduction alone. Fritsch and West in England have contributed 
a number of papers dealing with the frequency and reproductive 
activities of the algae in a number of pools and ponds. Some of the 
records of Fritsch cover a period of five years and are correspondingly 
valuable. In this country Copeland made a two-year study of the 
periodicity of the Spirogyras, and Brown published some records of 
the occurrence of algae in southern Indiana. 
As a result of these field studies there have developed two extreme 
points of view: Copeland came to the conclusion that his observations 
"offer overwhelming evidence in support of the view that the phe- 
nomenon of conjugation results not so much from external as from 
internal conditions," and "that Spirogyra has definite periods of 
growth and reproductive activity" ; Fritsch on the other hand assumes 
to account for all the phenomena of germination, vegetative develop- 
ment and reproduction on the basis of changes in the environment. 
He emphasizes especially the effects of temperature, light, and con- 
centration of medium, although he made no determinations of the 
actual concentration of the waters with which he dealt. 
The present paper is based on seven and a half years continuous 
records of the algal conditions in central Illinois. About 3,000 collec- 
tions have been analyzed. Particular attention has been given to 
the Zygnemales, the Oedogoniales, and the other filamentous forms. 
As a result there are notes on the occurrence of over three hundred 
species, and sufficient data to establish the periodicity curve of about 
half that number. Aplanospores, zoospores, zygospores and oospores 
have been recorded more than a thousand times in the course of the 
work. 
Our algae fall with few exceptions into six natural groups, based on 
the time of their germination, vegetative development, reproduction 
and dormancy (Fig. i). 
I. The Winter Annuals begin their vegetative activities in the 
autumn, increase these activities up to the time the ponds are frozen 
over, and pass the winter under the ice. They may develop further 
during protracted winter thaws and may even fruit. Their reproduc- 
tive activities culminate in March and April, although sexual spores 
