1202 Wisconsin Academy of Sciences, Arts and Letters . 
The variations in cleavage of the mother cell are little af¬ 
fected by external conditions. 
[When the autospores are motile they are influenced by ex¬ 
ternal conditions through the influence on the motility of the 
zoospores. 
The variations occurring in the cultures of the algae studied 
are not sufficient to warrant any assumption of widespread 
polymorphism among the algae. 
I wish to express my thanks here to Professor Charles E. 
Allen for his kind criticism during the progress of the inves¬ 
tigation and in the preparation of the manuscript. 
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