168 GROWTH HABITS OF PLANTS 



in submerged leaves and are present only on the upper surfaces of 

 floating leaves. Such stomata as are present have but slightly 

 cutinized walls and are almost always open. Protective features are 

 few or wanting. Cutin and cork rarely are developed below the sur- 

 face of the water, hairs are scarce, and the cell sap has a low osmotic 

 pressure. Conducting and mechanical tissues are also greatly re- 

 duced. The absence of protective features is, of course, not disad- 

 vantageous to the plants because absorption is easy and below the 



Fig. 73. —A marsh in California. The vegetation is abnost exclusively Scirpus 

 validus (great bulrush), a typical hydrophyte. (Photograph by H. L. Shantz. 

 Courtesy of H. L. Shantz and the U. S. Department of Agriculture.) 



surface of the water transpiration is practically absent. The sub- 

 merged portions of seed plants are usually covered with slime which 

 harbors communities of bacteria and other low organisms. The 

 aerial surfaces of floating organs, on the other hand, are usually 

 coated with wax and so are not easily wet. Vegetative reproduction 

 is highly developed in hydric habitats, while flowers and seeds are 

 less abundant than in most habitats. 



A swamp (Figs. 74 and 75) is a hydric habitat which differs from 

 a pond or lake in that the water table is just about at the surface of 

 the soil, though it may be a little above during wet seasons or a little 

 below during dry seasons. Some characteristic swamp plants are the 

 cattails (Typha), the reed (Phragmites) , the bulrush (Scirpus), etc. 

 The structural features of swamp plants are in part like those of 

 pond plants, especially in the reduced root systems and prominent 



