143 



lacusiris, Potamogeton fluilans, Nymphaea advena. (3) Confined to shallow water : 

 Pontederia cordata, Naias fiexilis, Nitella (a small moniliform species), Eleocharig 

 inter stincta, Eleoeharis pahistris, E. viutata, Cladium mariscoides, Vcdlisneria spiralis 

 and Potamogeton nutans. (4) Deep-water plants: Ceratophyllum, Myriophylluw, 

 Potamogeton lucens, P. amplifolins and P. pectinatus. 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 may be placed in the 

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

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

 Scirpi and Eleochari 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 Avith short stems and 

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

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

 plants. 



These hike jiliuits irith emcrsed leaves extend from the shore out to 

 where the Av.itor is about &,» feet deep. Among these are reckoned the 

 Scirpi and KUavlKiyi (with the exidanation 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 whleli compose it. as 

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

 count, be divided into two sti'ips; one including the shalloAA' water forms 

 and the other the deep water forms. Castalia and Xi/mpttocd. which l»e- 

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

 hicustris grows out farther, that is. to a depth of 6% feet, and it here 

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

 some of the longest culms liy^ t^et. Where Scirpus grows 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 arrangement in 

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



The Aquatics with finbmersed 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 groups — the short- 



