130 



LEAVES AND THEIR WORK 



Storage of Food and Water in Leaves. Leaves may be modified for 



the storage of food and water. Test an onion, which is a collection of 



thickened leaves closely wrapped to form what is called a bulb, for starch, 



sugar, and proteid. Squeeze any 

 fleshy leaves and notice the water 

 contained in them. The agave is a 

 desert plant in which the leaves have 

 become greatly thickened as a water 

 and food storage. 



Leaves modified for Use in Climb- 

 ing. Sometimes, as in the leaf of 

 the pea, a part of the leaf is modified 

 for the purpose of climbing. In this 

 case a part of the leaf, called the 

 tendril, becomes especially sensitive 

 to the stimulus of touch, and upon 

 touching an object slowly coils around 

 it. Almost any part of the leaf, or 

 indeed the entire leaf, may be modi- 

 fied to become a tendril. 



Reduced Leaves. Leaves may 

 be reduced to scales or lost al- 

 together. In the asparagus, what 

 seem to be tiny leaves are branches 

 which spring from the axils of the 

 true, very tiny, scalelike leaves. 



Leaves as 

 Insect Traps. 

 Most curious 



of all are the modifications of the leaf into insect 



traps. It frequently happens that the habitat of a 



plant will not furnish the raw food materials ne- 



cessary to form proteid food and to build proto- 



plasm. Nitrogen is the lacking element. The 



plant has become adapted to these conditions and 



obtains nitrogenous food from the bodies of insects 



which it catches. Examples of insect traps are 



the common bladderwort (utricularia), the Venus's 



flytrap (Dioncea muscipula}, the sundew (Drosera 



rotundifolia}, and certain of the pitcher plants. 



Bladderwort. The simplest contrivance for the 



taking of animal food by the leaf is seen in the 



bladderwort. Here certain of the leaves are modified into little bladders 



provided with trapdoors which open inwards. Small water-swimming 



crustaceans (as water fleas, etc.) push their way into the trap and there 



Bladderwort, showing finely dissected 

 submerged leaves bearing blades 

 which capture little animals. 



of sundew closing 

 over capt ured insect. 



