LECT. X.] DIRECTION OF THE LEAVES. 531 



per disk of it only be exposed to the light and 

 air, it is termed floating- (natans), as in the 

 White Water Lily, Nymphaea alba, floating Wa- 

 ter Plantain, Alisma natans, &c. : and when it is 

 surrounded on every side by the water, as the 

 majority of leaves are by the air, its direction is 

 denoted by the term sunk or immersed (submersa, 

 immersa, demersa), as in perfoliate Pond-weed, 

 Potarnogeton perfoliatum. Some aquatics have 

 leaves which are immersed and also leaves which 

 float, as, for instance, Various-leaved Crow-foot, 

 Ranunculus aquatilu, the beautiful white flow- 

 ers of which decorate our ponds in the spring 

 and summer months: others, as verticillate 

 Water-milfoil, have both immersed and emerging 

 leaves. In these and similar plants, it is curious 

 to remark the manner in which the form of the 

 leaf is modified by the medium in which it 

 is naturally placed: the leaves, for instance, of 

 Ranunculus aguatUis, which grow under the 

 water, are divided into capillary segments (a. a. 

 fig. 1, page 532), while those which float on the 

 surface are merely lobed and notched (b.J. In 

 plants even which are not aquatics, but which may 

 happen to be planted in water, we perceive the me- 

 tamorphose from the flat to the capillary leaves 

 taking place in the fresh shoots before they gain 

 the surface of the water, after which they assume 



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