WATER-PLANTS 51 



II. Floating Leaves. 



1. The Circular or Orbicular Type. — Leaves of this 

 kind float on the surface of the water — e.g., water-lilies, 

 frogbit {Hydrocharis Morsus-rance, Fig. 19), the floating 

 leaves of the water-buttercup {Ranuriculus aquatilis). 

 In some cases the leaf has an upturned margin, which 

 diminishes the risk of capsizing (the great Amazon water- 

 lily, Victoria regia). The petioles of these leaves are 



Fio. 18. — ^Formation op Brood-Bot) in Potdmogdon crispus. (About 

 Half Natdhal Size. After Kernbk.) 



To the left a bud still attached to plant, to the right the separate bud. 



usually elastic and very flexible, so that they can, by 

 coiling or uncoiling, adjust themselves to variations in 

 the depth of the water. 



2. The Long Floating Ribbon-Type. — This differs in 

 no respect from that previously described, except that 

 it is not submerged. It is found in Sparganium natans, 

 and in the floating manna-grass {Glyceria fluifans). 



Heterophylly (Gr. heteros, different ; phyllon, leaf). — 

 Some plants exhibit two types of leaves, one float- 

 ing and the other submerged, and the two appear 

 together on the same plant. Thus the water-buttercup 

 has finely - dissected submerged leaves, and broadly- 



