110 Lake Maxinknckee, Physical and Biological Survey 



inkuckee. The coefficient of the net has not been determined, so 

 that the total quantity of plankton has not been calculated. 



As almost the entire volume of plankton was above the thermo- 

 cline, which is about 35 feet deep, no relation between the vertical 

 distribution and the change in temperature was noted. 



THE PLANKTON SCUM OR WASSERBLUETHE 



In addition to the plankton studies carried on at the lake by 

 Professor Juday in 1899, and by Mr. Young in 1900, reported on 

 by them in the preceding pages, some attention was given to the 

 subject by Mr. Clark and Dr. Evermann whenever opportunity af- 

 forded. Some of their observations are here recorded. 



Almost every dweller in a region where lakes abound is familiar 

 with the annual collection of green scum over the surface or parts 

 of the surface of the lakes. This phenomenon is known the world 

 over wherever lakes are found. It is known in Germany as 

 "Wasserbluethe" and in parts of England as the "Flowering of the 

 meres." About Lake Maxinkuckee it is spoken of as "the lake 

 cleaning itself." It is, indeed, the same phenomenon as may be 

 observed everywhere, wherever there is a stagnant pool or dead 

 stretch of river. 



Time of appearance: — The plankton scum does not appear gen- 

 eral over the lake until late summer or early autumn. The prime 

 condition for its appearance, in addition to proper temperature and 

 favorable environment for the rapid development of the low forms 

 which compose it, is an unruffled water surface. It accordingly 

 makes its first appearance in quiet sheltered bays. The following 

 are brief notes as to dates of occurrence: 



September 30, 1900. Air dead calm ; flecks of foam scattered 

 over the lake, slowly drift shoreward, and are colored green. 



October 3. Green scum, mixed in with insect exuvise noted 

 near shore. 



October 5. No scum, though the water is full of diffused 

 Anabsena near the Deephole. 



October 15. At noon, considerable green coating of water near 

 shore in front of Arlington Hotel. 



October 17. Morning calm, with considerable scum ; by noon 

 nearly as dense as yet seen. 



November 2. Some scum on the east side and some on the 

 surface of the deep water, but none at shore. The lake was calm, 

 and gave an opportunity to observe the formation of the scum. 

 The observation was made near the Deephole from a boat. The 

 water was full of diffused algce (principally Anabama and 



