186 



BOTANY 



PART I 



stalk-like outgrowths (" tentacles "), the glandular extremities of which 

 discharge a viscid acid secretion (Figs. 214, 215). A small insect 

 which comes in contact with any of the tentacles is caught in the 

 sticky secretion, and in its ineffectual struggle to free itself only 

 conies in contact with other glands and is even more securely held. 

 Excited by the contact stimulus, all the other 

 tentacles curve over and close upon the captured 

 insect, while the leaf-blade itself becomes concave 

 and surrounds the small prisoner more closely. 

 In Pinguicula it is the leaf margins which fold 



FIG. 215. Digestive 

 gland from Drosera 

 rotundifolia. ( x 60. 

 After STRASBURGER.) 



FIG. 216. Utricularia vulgaris. A, Part of leaf with several 

 bladders (x 2). B, Single pinnule of leaf with bladder (x 6). 

 C, Longitudinal section of a bladder ( x 28) ; v, valve ; a, wall 

 of bladder. (A, B, after SCHENCK; C, after GOEBEL.) 



over any small insects that may be held by the minute epidermal glands. 

 In species of Utricularia (Fig. 216), which grow frequently in stagnant 

 water, small green bladders (metamorphosed leaf-segments) are found 

 on the dissected leaves. In each bladder there is a small quadrangular 

 opening closed by an elastic valve, which only opens inwards. Small 

 crustaceans can readily pass through this opening, but their egress is 

 prevented by the trap-like action of the valve, so that in one bladder as 

 many as ten or twelve crustaceans will often be found imprisoned at the 

 same time. The absorption of the disorganised animal remains seems to 

 be performed by forked hairs which spring from the walls of the bladder. 

 More remarkable still, and even better adapted for its purpose, is 



