143 



lacustris, Potamogeton ftuitans, Nymphaea advena. (3) Confined to shallow water: 

 Pontederia cordata, Naias jiexilis, Nitellu (a small moniliform species), Eleocharis 

 interstincta, Eleocharis palvstris, E. mutata, Cladium mariscoides, Vallisneria spirah'.-' 

 and Potamogeton natans. (4) Deep-water plants: Ceratopkyllum, Myriophyllum , 

 Potamogeton lucens, P. amplifolins and P. pecfinatus. Beyond this last group belongs 

 mostly the floating confervoid algae of the lake. 



A consideration of the habits of the plants just mentioned will show 

 at once how their forms correspond to their position. Each group men- 

 tioned have certain common characteristics, and maj- be placed in the 

 same ecological group. (1) The shore plants already mentioned generally 

 have stiff, stout petioles and stiff, generally rather thicli, leaves. (In the 

 Scirpi and Eleocharl the culms function as leaves.) They all have large 

 air tubes leading to the roots. This applies to all the lake-dwelling species. 



Growing near the shore in places are the aquatics with short stems and 

 the plant wholly submersed. Naias is a good type. They form a baud m 

 the center of a group which forms a wider belt, the emersed leaved lake 

 plants. 



These lake plants with emersed leaves extend from the shore out to 

 Avhere the water is about &/2 feet deep. Among these are reckoned the 

 Scirpi and Eleocharl (with the explanation above). These plants form the 

 broadest belt in the lake, and one reason for the breadth of their distribu- 

 tion is to be found in the variability of the species which compose it, as 

 has been dwelt upon somewhat fully above. This belt may, on this ac- 

 cotmt, be divided into two strips; one including the shallow water forms 

 and the other the deep water forms. Castalia and Nymphaea, which be- 

 long here, grow out to a depth of about five feet eight inches. Scirpns 

 lacustris grows out farther, that is, to a depth of 6^ feet, and it here 

 projects up out of the water about .5 feet, making the total length of 

 some of the longest culms 11% feet. Where Scirpus gi'OAvs out into deep 

 water it seems to exhaust itself in the effort to reach light and air, and 

 so they are generally few-fruited or wholly .sterile, with deadish brown 

 tips. They progress out into the lake by means of rhizomes, and at the 

 outer edges of the belt one can frequently note their an-angement in 

 straight lines, corresponding to the position of the root stock. 



The Aqnatics with Submersed Leaves. — It is difficult to fix the exact 

 limits of these plants with certainty, especially so that they could be rep- 

 resented on a map, for they do not form visible patches at the surface. It 

 is convenient, as said above, to divide them into two fp'oups — the short- 



