194 OF AQUATIC PLANTS. 



the importance of shading and watering plants 

 newly removed, cuttings, grafts, &c. and on 

 the other hand the benefit of heat and air to 

 promote due perspiration and evaporation. 



The perspiration of aquatic plants seems to 

 be remarkably copious. Of these some grow 

 constantly immersed in the water, as most 

 species of Potamogetou, Pond-weed, E?igl. 

 Bot. t. 168, 297, 376, &c. Their leaves 

 are peculiarly vascular, and dry very quickly 

 in the air, withering in a very few minutes 

 after exposure to it. Their absorbing power 

 seems equally great, so that they appear to 

 be continually, in their natural situation, im- 

 bibing and giving out a quantity of water 

 much greater than has been observed in land 

 plants. Other aquatics, as the Nymphcece, 

 Engl. Bot. t.\59, 160, float with only the 

 upper surface of their leaves exposed to the 

 air, which surface is so contrived that water 

 will scarcely remain upon it. These leaves, 

 though extremely juicy, dry with great ra- 

 pidity, as does every part of the plants when 

 gathered. It is probable that they imbibe 

 copiously by their under sides, and perspire 

 by the upper. 



