Ranunculus 



Potamogeton 



Sagittaxia 



LEAVES IN AIR AND IN WATER 



The deeper the leaves of the water crowfoot are submerged, the more divided up 

 they are. For a given amount of tissue, finely divided leaves have a greater absorb- 

 ing surface. Pondweeds and arrowheads bear broad leaves in the air and long 

 ribbon-shaped leaves in the water 



water filling the soil spaces keeps the roots submerged too long. The roots 

 of rice are fine and threadlike, exposing much surface through which an 

 adequate supply of oxygen is obtained from the surrounding water. 



If the water table is near the surface as after prolonged rains in the early 

 summer, corn roots, for example, do not penetrate very far into the soil. 

 Then if a drought follows, the crop suffers badly, for the shallow root- 

 system cannot reach the lower water levels, and the plant quickly dries out. 

 On the other hand, when the early summer is exceptionally dry, the young 

 roots grow deeper, so that a prolonged drought later in the season is not so 

 destructive. Alfalfa will not thrive in a soil that is not well drained, for the 

 roots "drown". 



Plants growing in swamps, where the level of the water is rather con- 

 stant, have shallow root-systems ; and they breathe through the portions that 

 extend above the water. 



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