CHAPTER XLVI 



UNDER-WATER ENVIRONMENTS 



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Numerous kinds of plants live continuously under water. Many epi- 

 phytes, on the other hand, grow in a medium of air and are in contact 

 with water only during rains or when covered with dew. Even a rooted 

 plant in dry uplands grows almost entirely in the atmosphere which 

 surrounds its tops and fills the spaces between the particles of the soil. 

 Except for short intervals after rains, its root system in summer is in 

 contact only with thin films of water held by the soil particles, and much 

 of it is exposed to the soil air. 



Fig. 267. An abrupt transition in habitats and vegetation. 



Other species of plants live partially submerged in the shallow water 

 of marshes and swamps between uplands and near the borders of 

 oceans, lakes, and streams (Fig. 267). Some of them are limited to areas 

 in which the water level fluctuates with the rains and tides. Many plants 

 can endure partial submergence for limited periods of time, and many 



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