LEAVES: MODIFICATIONS 



95 



Fig. 80. 

 Leaf of pitcher plant (Sarracenia). 



leaves of insectivorous plants, like the Venus's flytrap, the sundew 

 (see paragraph 155), and the pitcher plants, of which a good 

 example is the common pitcher plant of our 

 sphagnum moors. Here the leaf is modified into a 

 pitcher-shaped structure, broadened near the middle 

 and narrowed somewhat near the free end, where 

 there are on the inside of the pitcher numerous 

 bristle-like hairs pointing downward. Certain in- 

 sects which enter the leaf are prevented from crawl- 

 ing out by these hairs, and after a while they fall 

 into the water at the bottom of the pitcher and die. 

 153. Reduction of leaves to 

 bracts or scales on the flower 

 shoot. Reduced leaves on the 

 flower shoot are often green, small 

 and thin, as in the bell flower, 

 marigold, etc. These are termed brads. On some flower shoots 

 the bracts are broad and colored like the petals of some flowers 

 as in the flowering dogwood. Bracts of the flower shoot are 

 sometimes termed scales 

 when they are more or less 

 rigid and thickened, as in 

 the heads of some com- 

 posites. The thickened 

 bases of the scales on the 

 flower head of the " arti- 

 choke" (Cynara scolymus) 

 are edible. 



154. Irritability of 

 tendrils and twining 

 stems. When a tendril 

 or a twining stem, as it 

 slowly swings around, 

 comes in touch or contact with some object, this contact stimulus 

 causes it to bend at this point bringing new points in contact so 

 that the tendril or stem then coils around the object of support. 



Fig. 8 1. 



Leaf of Venus flytrap 

 (Dioniea muscipula), 

 showing winged petiole 

 and toothed lobes. 



Fig. 82. 



Leaf of Drosera ro- 

 tundifolia, some of the 

 glandular hairs folding 

 inward as a result of a 

 stimulus. 



