LEAVES AND THEIR WORK 



131 



die, perhaps of starvation. Bacteria, causing decay, soon break down 

 their bodies into soluble substances, the nitrogenous portion of which 

 is absorbed by the inner surface of the bladders and used by the 

 plant as food. 



Venus's Flytrap. — In the Venus's flytrap, a curious plant found in 

 our Southern states, the apex of the leaf is peculiarly modified to form an 

 insect trap. Each margin of 

 the leaf is pro\'ided with a 

 row of hairs ; there are also 

 three central hairs on each 

 side of the midrib. The 

 hairs are sensitive to a 

 stimulus from without. The 

 blade is so constructed that 

 the slightest stimulus causes 

 a closing of the leaf along 

 the midrib. The surface of 

 the leaf is provided with 

 many tiny glands, which pour 

 out a fluid capable of digest- 

 ing proteid food. Thus an 

 insect, caught between the 

 halves of the leaf blade, is 

 held there and slowly digested. 



Sundew. — In the sundew 

 the leaves are covered with 

 long glandular hairs, each of 

 which is extremely sensitive 

 to the stimulus of any nitrog- 

 enous substance. These 

 hairs exude a clear, sticky 

 fluid which first renders 

 more difficult the escape of 

 the insect caught in the hairs, 

 and then digests the nitrog- 

 enous parts of the insect 

 thus caught. 



Pitcher Plants. — The common pitcher plant has an urn-shaped leaf 

 which is modified to hold water. Many small flies and other insects 

 find their way into the pitcher and are eventually drowned in the cup. 

 Whether the plant actually makes use of the food thus obtained is a 

 matter unsettled, but some tropical forms undoubtedly do use the caught 

 insects as food. 



Pitcher plant : a, leaf ; 6, cross section ; c, longi- 

 tudinal section. Note the insects at the bottom, 

 and the inward-pointing hairs at the top. 



