. hinrnait lislurit's Sociily. 103 



is a spring \\liii.-li I haw tcslcd about a niik' from (.jarviii Lake 

 whose tcnii)craturc is aboiU 50 tlegrecs. 



Mr. Whitakcr: Have you ever uiadc any observations with 

 reference to the abundance of i)lants at the bottom of the lake? 



I'rol. l')irg-e: No; I have not had time to take that up. 



Mr. Whitaker: Do }ou know at what depth in these lakes the 

 growtii of plants stops practically? 



Prof. Birg^e: It wouldn't get down to that cold lower water, 

 anyway. You don't get a great many springs in the bottom of a 

 lake. As a matter of fact, the spring would be more likely to 

 come out near the level of the lake than further down. The spring 

 comes from the head of water that is in the soil. When you get 

 down l)elow the level of the soil water there is less head of water. 

 So the spring will ordinarily work out of the edge of the lake or 

 in shallower water. 



]\Ir. Whitaker: 1 believe the investigation of Lake St Clair 

 showed that the bottom of the lake was covered with a perfect 

 mat of chara. As I understand it. on all lakes there is a certain 

 shore zone, bare of plants: made barren by the action of the 

 waves, which prevents the growth of plants. 



Prof. Birge: Not in these very small lakes. In Mendota. ex- 

 cept at sheltered places, the wind affects the plants to a depth of 

 3^ to 4 feet. 



Mr. Pcabody: What is the greatest depth that the action of 

 the wind reaches so as to modifv the temperature? 



Prof. Birge: So far as I know, its action extends to the 

 greatest depths of oin- inland lakes, (ireen Lake is 2^^ feet in 

 depth. The temperature of the water at the bottom rises during 

 the spring and falls during the late autunm. I cannot conceive 

 that this change is due to anything but the action of the winds. 



Mr. f»owcr: I think your statement explains why some of the 

 Great Lakes are more prolific as to production of fish than 

 others. I understand that the greater amount of water life, the 

 greater vegetation, the greater amotmt of fundamental 

 life, the larger the higher forms of life. Of our Great Lakes there 

 is no lake that begins to compare with Lake Erie in the amount 

 of fish caught. There are large areas that are sheltered, but still 

 subject to the action of the wind all the \car. in a degree: that 

 accounts for the reason why the most productive places are the 

 bavs : take all the bavs on the Canada shore, and Sag- 



