140 



BOTANY 



Leaf of sundew closing 

 over captured insect. 



trap. Each margin cf the leaf is provided 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 digesting proteid food. Thus an in- 

 sect, caught between the halves of che 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 nitrogenous substance. 



These hairs exude a clear, sticky fluid which first ren- 

 ders more difficult the escape of the insect caught in 



the hairs, and then digests 

 the nitrogenous parts of the 

 insect thus caught. Charles 

 Darwin, in a series of experi- 

 ments, found that these hairs 

 do not respond to the stimu- 

 lus of falling raindrops, but 

 that a bit of hair weighing 

 only y 8 y JO- of a grain is enough 

 to cause the slight bending of 

 the hairs. 



Pitcher Plants. — The 

 common pitcher plant has an 

 urn-shaped leaf which is modi- 

 fied 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 un- 

 settled. In a tropical form, 

 called Nepenthes, the petiole 

 of the leaf forms the pitcher, 

 the blade of the leaf forming 

 a kmd of lid. In the fuU- 

 grcwn plants this lid stands 



Pitcher plant; a, leaf; 6, cross section; c, longitudinal open, perhaps as an attrac- 

 section. Note the insects at the bottom, and the -• j. • x tt i ^ 



inward-pointing hairs at the top. tion to msects. Honey glands 



