HOW PLANTS ARE INFLUENCED 



339 



erless plants) were originally land -plants which 

 were forced by competition to take to the streams 

 and lakes. Some of them still possess the power 

 to live on land if the water falls away, while others 

 can live only in water and quickly perish when left 

 without it (Horn wort, Water-lily, Pondweed, etc.). 

 The water-plants in general show exactly opposite 

 features to those already enumerated as characteristic 

 of desert -plants. They have a large exposed surface, 

 thin cuticle, no waxes, varnishes, resins or hairs on 

 the surface, a minimum amount of woody fiber, very 

 large air-spaces and poorly developed palisade. 



a 



195. Leaves of the Water-buttercup: (a) water-leaf, (6) air-leaf. 



Stomata occur, as a rule, only on surfaces which are 

 directly exposed to air (Fig. 196). 



Water-plants have usually a very poorly developed 

 root- system : many of them have no roots at all, but 

 float about on the water, sinking to the bottom on the 



