206 



SECRETION AND EXCRETION 



In the pitchers of the genus Nepenthes unstalked digestive 

 glands occur on the inside near the bottom. These pour forth 

 an abundance of a mucilaginous digestive fluid the water for 



which is supplied to 

 the gland by a bundle 

 of tracheids extending 

 close up to the base of 

 the gland. 



The most highly- 

 differentiated glands 

 are found on the leaves 

 of Drosera rotundifolia 

 (Fig. 105). Here the 

 gland proper, which is borne at the apex of a slender stalk, is 

 composed of a bundle of tracheids surrounded by three layers 

 of cells. The outer two layers seem to be especially concerned 

 in producing the secretion. The cuticle is permeable, and ordi- 



upper 



Fig. 115. — Glands from Pinguicula. A 

 surface of leaf showing long-stalked gland at m, and 

 short-stalked gland at m. B, cross section through a 

 short-stalked gland. (.4, after Kerner, and B, after 

 Haberlandt.) 



Fig. 116. — Different forms of crystals of calcium oxalate. .4, from the petiole of Begonia 



manicata. (After Frank.) 



narily an acid, sticky secretion is excreted at the surface in which 

 the feet of insects alighting on the surface become entangled. 

 The capture of an insect stimulates the glands to secrete and 



