CHAPTER XLIX. 



ZONAL DISTRIBUTION OF PLANTS. 



473. 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 definite areas occupied 

 by certain plants. Figure 

 257 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. 



474. Zonal arrangement. 

 — This arrangement of plants 

 under such environmental influences is termed ' ' zonal distribution 

 of plants. ' ' The slope where this photograph was taken is so 



306 



Fig. 256. 

 Sagittaria variabilis. 



