MODIFICATION OF THE ORGANS OF PLANTS 85 



Besides the many species found on moors and culti- 

 vated land and in woods, there are other kinds 

 of Ranunculus E. sceleratus, for instance which 

 grow by the water-side. In this species it is not 

 uncommon to find floating leaves, and leaves which 

 wholly emerge from the water, growing on the same 

 stem. In other species, such as Ranunculus 

 hederaceus, there are seldom any but floating leaves. 

 Among the numerous varieties of Ranunculus aqua- 

 tilis there are some which, in addition to the floating 

 leaves, have also some leaves which are completely 

 submerged and deeply dentated ; in other varieties 

 of the same species there are only slightly dentated 

 leaves, while in Ranunculus flidtans the leaves are 

 all fringed. 1 



(c) In a submerged plant which is to be found in 

 Madagascar, Ouvirandra fenestralis (fig. 47), the 

 diminution in volume, compared to the surface, is 

 effected in a different manner. After the leaf has 

 developed in the" ordinary way, all the parts of the 

 leaf in between the veins of the blade disappear. 

 This results in the blade being reduced to a delicate 

 piece of network, consisting entirely of communicat- 

 ing veins accompanied by adjacent assimilative cells. 



4. Adaptation to defence against ants. In the 



1 Ranunculus sceleratus grows by the water-side ; R. hederaceus 

 is to be found on marshy ground, the internodes and petioles being 

 quite short ; R. aquatilis grows in shallow water, and the internodes 

 are of sufficient length to raise the flowers out of the water ; R. 

 fluitans grows in strongly-running streams, so that floating leaves 

 would be useless. 



