100 



PLANT BIOLOGY 



sticky hairs that close over the insect ; the Venus's flytrap 

 of the Southern states, in which the halves of the leaves 



close over the prey like the jaws 

 of a steel trap ; and the various 

 kinds of pitcher plants that col- 

 lect insects and other organic 

 matter in deep, water-filled, flask- 

 like leaf pouches (Fig. 119). 



The sundew and Venus's fly- 

 trap are sensitive to contact. 

 Other plants are sensitive to the 

 touch without being insectivo- 

 rous. The common cultivated 

 sensitive plant is an example. 

 This is readily grown from seeds 

 (sold by seedsmen) in a warm 

 place. Related wild plants in 

 the south are sensitive. The 

 utility of this sensitiveness is not understood. 



Parts that Simulate Leaves. We have learned that 

 leaves are endlessly modified to suit the conditions in which 

 the plant is placed. The most marked modifications are in 

 adaptation to light. On the other hand, other organs often 

 perform the functions of leaves. Green shoots function as 

 leaves. These shoots may look like leaves, in which case 

 they are called cladophylla. The foliage of common 

 asparagus is made up of fine branches : the real morpho- 

 logical leaves are the minute dry functionless scales at the 

 bases of these branchlets. (What reason is there for calling 

 them leaves?) The broad " leaves" of the florist's smilax 

 are cladophylla : where are the leaves on this plant ? In 

 most of the cacti, the entire plant body performs the func- 

 tions of leaves until the parts become cork-bound. 



FIG. 119. THE COMMON 

 PITCHER PLANT (Sarracenia 

 purpured) of the North, show- 

 ing the tubular leaves and the 

 odd, long-stalked flowers. 



