A GREEN EEAF 



69 



encircled with dark cells, and situ<ited at intervals 

 round the maro-in of the section, are resin ducts 



Yii^. 46. The curious stiuctuie (A the pine-tree leaf 



similar in structure to those found in the pine- 

 wood stem. 



In plants like the waterdih', whose leaves float 

 on the surface ot the water, a special arrany-ement 

 is required. The spony-y 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 cr\'stals 



