84 SMITHSONIAN INSTITUTION 



more than 800 lakes, more water area than land.. In this, one of the 

 world's most concentrated lake districts, one may conveniently visit 

 several lakes in a morning- and study his materials in the afternoon. 



But what, after all, is so interesting about a lake? To the vacation- 

 ist who frequents this region, a lake is a fairly sizeable body of water, 

 fixed and unchangeable year in and year out, which should yield what- 

 ever type of fish he may choose to angle for. To a biologist, on the 

 other hand, a lake is a highly particular and sensitive body of water, 

 dynamic and variable, and teeming with life of a very unstable and 

 changeable nature, no more capable of producing a bumper crop of 

 fish unsuited to it than a sandhill farm is capable of producing a heavy 

 crop of corn. And no two lakes are precisely alike ; each has a per- 

 sonality of its own. 



The kind of fish depends upon the kind and abundance of a myriad 

 of smaller organisms upon which they feed, and these in turn upon the 

 kind and abundance of small plants serving them as food, the plants 

 upon chemical food materials dissolved in the water, and all of these 

 upon the configuration of the lake basin, the surrounding soils from 

 which its waters drain, the amount and quality of solar radiation for 

 plant growth, and many other complicated factors. 



In years of diligent work Drs. Birge and Juday have analyzed and 

 tabulated on readily accessible cards the chemical constituents of 540 

 of these lakes, thereby giving intimate and comparative knowledge of 

 their characteristics, and aiding selection of particular lakes for spe- 

 cial experiments ; as it were, a vast series of aquaria already set up 

 for experimental study. 



With this well-adapted background, I have thus far obtained diatom 

 collections from about 150 of the lakes, representing all diverse types. 

 These collections, from lakes often superficially very similar, show a 

 considerable variety of species, with evidence that " survival of the 

 fittest " plays an important role ; often slight and subtle differences 

 in proportion of chemical substances in the water, or in some physical 

 factor such as temperature or light penetration, favor one species and 

 give it dominance over another. 



Some lakes are probably much the same today as the day they were 

 formed, others have evolved to the stage of a nearly filled bog. Some- 

 times the latter are the more interesting, but often the most inacces- 

 sible. Frequently we could not get a light skiff through the scrub pine 

 and over the bog margin to a lake, and it was preferable to use an 

 inflated rubber boat somewhat resembling a huge doughnut. Footing 

 in it was always insecure, and one stroke of the short oar would spin it 



