FOREWORD 



It is tlie policy of the American Associ- 

 ation for the Advancement of Science to 

 pnblish symposia presented at its meetings 

 that "are on subjects of such importance 

 and are of such quality that it can not 

 afford not to publish them." The symposia 

 heretofore published by the Association be- 

 cause they were deemed to measure up to 

 these standards have been The Cancer 

 Prohlem (1937), Tnherculosis and Leprosy 

 (1938), Applications of Surface Chemistry 

 in Biology (1938), Recent Advances in 

 Chemical Physics (1938), Syphilis (1938), 

 and Mental Health (1939). 



This symposium on Problems of Lake 

 Biology was organized by the Limnological 

 Societv of America, an affiliated society of 

 the Association. In providing facilities for 

 presenting the symposium and in publish- 

 ing and distributing it, the Association as- 

 sists one of its affiliated societies in advanc- 

 ing the interests of a relatively new field of 

 science. The great value of a systematic, 

 comprehensive and documented survey of a 

 rapidly developing science is obvious, for 

 it establishes a solid foundation for future 

 work and presents an outline of a region 

 largely to be explored. This symposium, 

 which was planned by a committee of dis- 

 tinguished specialists in the field, has these 

 ciualities. 



Perhaps no other biological subject in- 

 volves a greater variety of interrelated fac- 

 tors than lake biology. On the one hand, 

 there are such physical factors as the size, 

 shape and depth of the lake, the source and 

 temperature of its water, its drainage, the 

 winds that ruffle its surface, the hydrostatic 

 pressures at various depths, and all the 

 complexities of the light of different wave 

 lengths it receives at various depths during 

 the daily and seasonal cycles. The chemi- 

 cal factors are no less numerous and im- 



portant, among whicli are the water content 

 of diffused oxygen, carbon dioxide, nitrogen 

 and hydrogen ionizations, and the amounts 

 in solution of compounds of calcium, iron, 

 silicon, phosphorus and other elements. In 

 addition, there are numerous ever-changing 

 and interacting organic compounds. 



Finally, there is the cooperating and 

 competing life itself, both plant and animal, 

 both microscopic and macroscopic. In 

 some cases the cooperation is direct — or- 

 ganism with organism or classes of organ- 

 isms vrith other classes; the same is true of 

 competition. In other cases the coopera- 

 tion or competition is indirect — certain or- 

 ganisms or classes of organisms affecting the 

 environment, physical, chemical or biologi- 

 cal, to the advantage or disadvantage of 

 other organisms or classes of organisms. 

 In the light of the discussions in this vol- 

 ume, lakes themselves may be regarded in 

 a sense as organisms having innumerable 

 interesting characteristics and entrancing 

 life histories. 



Anyone not familiar with lake biology 

 will be impressed with the great variety 

 and abundance of life in lakes and in the 

 sands along their shores. For example, at 

 a distance of 150 centimeters from the 

 shores of certain lakes which were studied 

 there were, on the average, in ten cubic 

 centimeters of sand 4,000,000 bacteria, 

 8,000 Protozoa, 400 Rotatoria, 40 Copepoda, 

 and 20 Tardigrada. In a lake of moderate 

 dimensions there are probably more indi- 

 vidual living organisms than there are ver- 

 tebrate animals on the whole earth. Natur- 

 ally this abundant and interesting life in a 

 complex, varied, ever-varying, and easily 

 accessible environment offers rare oppor- 

 tunities for investigating fundamental 

 l^roblems of the organic world. 



F. R. MOULTON 



