CHAPTER LIV. 



ZONAL DISTRIBUTION OF PLANTS. 



712. On the margins of lakes or ponds, where the slope is 

 gradual from the land into the water, one often has an oppor- 

 tunity to study the relation 

 of various plants to different 

 conditions of soil and water. 

 In rowing near the south shore 

 of Lake Cayuga, I have often 

 been impressed with the defi- 

 nite areas occupied by certain 

 plants. Figure 492 is from a 

 photograph, taken from the 

 boat, of the shore distribution 

 of these plants. The most 

 striking feature here is the 

 grouping of certain kinds of 

 plants in definite lines or 

 zones. Here the limitations 

 of the zones are quite distinct, 

 so that the transition from 

 one zone to another is quite 

 abrupt, though there is some 

 mixture of the kinds at the 

 zone of transition, or tension- 

 line. 



713. This arrangement of 

 plants under such environ- 

 mental influences is termed " zonal distribution of plants." The 



400 



Fig. 493- 

 Sagittaria variabilis. 



