150 



DIGESTIVE GLANDS 



TYl. 



The tentacles of the Sundew (Drosera) are much more elabo- 

 rate, being supplied with a vascular bundle which extends into 

 the slightly enlarged tip. In the latter the bundle is enveloped 

 by three distinct layers of cells, of which the innermost is thick- 

 ened after the manner of an endodermis, while the two outer 

 layers which contain the crimson pigment are those actually 

 concerned in secretion ; the superficial one has a palisade-like 

 structure. The tentacles of the Sundew, like many other digestive 

 glands, serve not only for the secretion of the digestive fluid, 



but also to 

 absorb the pro- 

 ducts of its 

 action; in addi- 

 tion they pro- 

 duce the ad- 

 hesive mucilage 

 which forms a 

 thick glistening 

 layer over the 

 head of the 

 tentacle. 



The Bladder- 

 wort (Utricu- 

 laria) is stated 

 to secrete no di- 

 gestive fluid, the 

 four-armed hairs 

 which occur on 

 the inner surface 



of the bladders serving solely for the absorption of the products 

 of decay of the minute bodies of the entrapped animals. 



Various digestive ferments are likewise secreted by the sur- 

 face of the cotyledons of albuminous seeds whereby the food- 

 substances in the endosperm are changed into a diffusible form. 

 In general there is no differentiation of a special secreting layer, 

 although in Grasses the palisade-like epidermal cells of the 

 scutellum, in contact with the endosperm, are glandular in char- 

 acter. These same cells are also concerned in the absorption 

 of the digested food-substances. 



FIG. 75. Transverse section through a small part of 

 the leaf of the Butterwort (Pinguicula), showing 

 the short digestive glands (d.) and a mucilage- 

 secreting hair (m.). 



