U. S. B. F.— Doc. 923. 



Fig. 13.— Another portion of the same pond (A 3) shown in figure 12, illustrating the character of the 

 shore and emergent vegetation. 



Fig. 14. — Portion of smaller pond (B), University of Pennsylvania, showing character of marginal 

 vegetation. The Lemna mat which later in the season completely covers this pond has not yet 

 appeared. This pond was used for Gambusia experiments. 



