A GREEN LEAF 



69 



encircled with dark cells, and situated at intervals 

 round the margin of the section, are resin ducts 



Fig. 46. The curious structure of the pine-tree leaf 



similar in structure to those found in the pine- 

 wood stem. 



In plants like the water-lily, whose leaves float 

 on the surface of the water, a special arrangement 

 is required. The spongy portion of the leaf-cells 

 becomes largely developed, and great air cavities, 

 which act as buoys, make their appearance. In 

 these air cavities curious and beautiful crystals 



