154 OHIO STATE ACADEMY OF SCIENCE. 



It extends in typical places from a depth of 5 feet on the outer 

 side, where it is bounded by water-lilies, to a depth of 10 feet or 

 more on the inner side. At the north end where conditions are 

 ideal the zone is 15 feet wide between the 5 and 10-feet limits. 

 On the west side it is 20 feet between these limits. Beyond the 

 10- feet limit the depth increases very rapidly. The water of the 

 lake is considerably colored, which must have an important effect 

 on the submerged vegetation. All the plants in this zone have 

 slender, wand-like stems with narrow and slender or much dis- 

 sected leaves or branches. They are all highly specialized and 

 thoroughly adapted to their habitat. They appear to occupy the 

 ground because no other plants are able to follow. On the outer 

 side they are pushed back by the water-lilies as far as these are 

 able to invade the water. The typical plants are : 



Potamogeton zosteraefolius Schum. 



" lucens L. 



Ceratophyllum demersum I,. 

 Myriophyllum sp. 

 Chara sp. 



Other species are : 



Potamogeton foliosus Raf. 

 " pectinatus L. 



Naias flexilis (Willd.) R. & S. 

 Zannichellia palustris L. 



On the surface are frequently found the free-floating duck- 

 weeds : 



Spirodela polyrhiza (L,.) Schl. 



Lemna minor L. 



Wolffia columbiana Karst. 



2. Water-lily Zone. This is a Nymphaea-Castalia zone, 

 the two plants that give character to the society being Nymphaea 

 advena Soland. and Castalia odorata (Dryand) W. & W. It is 

 said that the Castalia was introduced artificially, but it is now 

 well established. At the north end the zone is 40 feet wide and 

 extends from water five feet deep to two feet deep. On the west 

 side it is 28 feet wide. This is a very striking zone on account 

 of the large, upright leaves of Nymphaea. The comparative 

 absence of Nymphaea in water shallower than two feet must be 

 accounted for on the grounds of a severe struggle with the plants 



