24 



PLANT RELATIONS. 



one. Perhaps the most complete fitting together of leaves 

 is found in certain ivies, where a regular layer of angular 

 interlocking leaves is formed, the leaves fitting together like 



Fig. 18. A plant (Pellionia) with drooping stems, showing how the leaves are all 

 brought to the lighted side and fitted together. 



the pieces of a mosaic. In fact such an arrangement is 

 known as the mosaic arrangement, and involves such an 

 amount of twisting, displacement, elongation of petioles, 



