[Chap. X 



HEREDITARY DIFFERENCES IN LEAVES 



91 



Fig. 48. Cross sections of leaves of bluegrass (A) and beach grass (B). The 

 mechanism which unfolds and folds these leaves may be seen as enlarged upper 

 epidermal cells at the base of each sinus. 



water stomates are formed. Air cavities make up a large proportion of 

 the volume of the leaves of water hyacinth, arrowhead, and cattail. 



Insectivorous leaves. Most unusual leaf forms occur in the sundews, 

 pitcher plants, and the Venus's-flytrap. These are usually grouped to- 

 gether as insectivorous plants because small insects may be caught among 

 the sticky glandular hairs of the sundew leaves, and on the snap-trap 

 blades of the flytrap. Insects large and small fall into the "pitchers" 

 ( Fig. 49 ) . In several of these plants it has been shown that soluble sub- 



