44 MICHIGAN ACADEMY OF SCIENCE. 



lY. A zone of Carer and ^Si)lia</iti(iii from six to twenty-five feet wide 

 and extending around nearly the entire circumference of the lake, its 

 characteristic plants are Carcx pUforniis. L., Sphaf/nnm, and Potcntilla 

 palnstris. Scop. The outer edge of this zone is two or three inches beloAv 

 water level, the inner edge is five or six inches above water; lying so 

 close to the actual water level, this zone is of course "saturated with 

 M'ater and the tough mat of sedges is little better than a floating 

 island. 



V. A zone of Sali.r and Popiiliis from ten to forty feet wide extends 

 entirely around the lake and stands from three to twenty-four inches 

 above the preceding zone. Some of its characteristic plants are Salix 

 alha, L., S. luc'uhi, Muhl., »S'. iin/rtiJloidcs, L., Popiihis inimilohlcs, Michx. 

 and JJhmis amcricana, L. 



VI. A zone of (iiamincw and Coi)iposit<r lies just outside of the last 

 zone and is from six to thirty" inches above it. Its most characteristic 

 plants are l^pifea salicifolia, L., Eupatoriuiti pcrfoVKitinn, L., and Ruiiic.p 

 ohtiisifoliiis, L. 



The greatest admixture of terrestrial plants occurs on the north and 

 southeast shores where the struggle between plants has been greatest 

 for some time. The list of plants now contains representatives of thirty- 

 two orders. 



A studj' of the different zones shows that their jiositious are not per- 

 manent, but that they are slowly encroaching upon the lake and filling 

 it. The Kymphea zone is a more active land-forming agent than either 

 the Chara or I'otamogeton zone. The leaves and petioles of- Xuphar 

 projecting above the surface of the water catch and hold most of the 

 twigs, plants and leaves which are blown into the edge of the lake, 

 until they become water-logged and sink. The debris resulting from 

 the decay of the ])lants added to those which they have captured all 

 goes to build up the bottom. Whenever in any place the bottom is 

 not more than four or five inches below the surface of the water, the 

 sedges begin to move out and occupy the territory thus ])iepared for 

 them. Perhaps at first they only send out a few skirmishers which 

 occupy the top of a muskrat's mound; generally, however, they ad- 

 vance in an unbroken, solid line and cover the soft muck with a tough, 

 quaking mat of vegetation. As the Carex zone crowds upon the 

 Xymphea zone, so is it in turn crowded upon by the Salix zone. 



On steep gravelly banks and i)laces where conditions are unfavor- 

 able for the growth of Xuphar, this process of filling does not occur, 

 because the preliminary process of filling by decay cannot take ])lace. 

 the result is that the shore line in such places is quite well marked and 

 permanent. 



A few rods south of the lake is the site of the "dead lake," mentioned 

 above, which may tlirow some light on the life history of the present lake. 

 There is an elli})tical dejiression. in ihe center of which is a group of 

 sedges and ferns surrounded by a wide belt of willows, oTitside of these 

 again, a zone of grasses and terrestrial jtlants. It a]»])ears as if this had 

 been the site of a former lake which had been steadily encroached upon 

 by the sedges, in the manner previously described, followed in turn by the 

 willows as soon as Hie sedges had formed a moi-e or less firm soil. The 



