150 



DIGESTIVE GLANDS 



m. 



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 



FIG. 75. Transverse section through a small part of 

 the leaf of the Butterwort (Pinguiculd) , showing 

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

 secreting hair (m.}. 



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. 



