272 THE BIOLOGY OF FLOWERING PLANTS 



looked 



Fig. 38 

 2 nat 



on as serving not only to support the plant as a whole, 



but in particular as supporting 

 the considerable weight of the 

 large pitchers half filled with 

 liquid. 



The edge of the pitcher 

 is strengthened by a strong 

 rounded and ribbed rim in 

 which vascular tissue predomi- 

 nates. The mouth is thus 

 kept full open. The structure 

 of the inner wall is complex. 

 It is usually divided into two 

 sharply differentiated zones, the 

 upper covered by an unwettable 

 wax coating, the lower ex- 

 tending halfway up the pitcher, 

 or, in some cases, nearly to the 

 rim, glandular and glistening. 

 The glands are multicellular, 

 half sunk in epidermal cavities, 

 and secrete the watery fluid 

 which is found in the pitcher. 

 Glands are also found on the 

 under side of the Hd and about 

 the rim, and these are said to 

 secrete nectar which attracts 

 insects. 



The non-glandular upper 

 zone of the pitcher consists of 

 smooth cells, among which are 

 some projecting over the sur- 

 face with the free part pointing 

 downwards. These are modi- 

 fied and abortive stomatal 

 guard cells. This zone serves 



as the trap for any insect which 

 -Phcher of Nepenthes. ^^^ ^^^^^^^ ^^ ^^ j^ -^^ ^^^^^^^^ 



