270 THE BIOLOGY OF FLOWERING PLANTS 



Goebel mentions that it is used as " fly-paper " in PortugaL 

 The stimulation of the glands induces increased secretion 

 but no movement ; the capture is purely passive. Roridula, 

 a Cape genus, and Byblis with two Australian species, are 

 also passive. Doubts have been expressed as to the 

 capacity of the former to digest an animal diet. 



A diff"erent type of mechanism is exhibited by Dioneea 

 muscipula and Aldrovanda vesiculosa. The former occurs 

 in bogs in the Southern Atlantic States of America. Its 

 leaves are arranged in a rosette. Each possesses a winged 

 stalk and a blade, the margins of which bear long fine teeth. 

 On the upper surface of each half of the blade are three 

 multicellular bristles with jointed bases. If one of these 

 bristles is touched the two halves of the leaf snap together 

 in less than a second, the marginal teeth interlock, and the 

 insect or small worm which has released the mechanism is 

 securely trapped. The movement is due to turgor changes, 

 and is fixed by growth (Brown, 1916) : it is accompanied 

 by electrical phenomena similar to those which occur in 

 stimulated animal muscles (Burdon- Sanderson, 1882, 1889). 

 The six bristles alone, and no other parts of the leaf, are 

 sensitive to the shock stimulus. Brown and Sharp (1910) 

 have shown that, at ordinary temperatures, two successive 

 touches within about 20 sees, are required to produce a 

 reaction. Movement follows the second touch immediately. 

 At high temperatures (35° C.) a single touch suffices. 

 The numerous sessile glands which cover the surface re- 

 spond to chemical stimulus by pouring out a digestive 

 secretion. After resorption of the products of digestion the 

 leaf opens, by growth, and is capable of renewed action. 

 This movement is, with that exhibited by the leaves of 

 Mimosa pudica, the most striking in the plant kingdom. 



The European Aldrovanda vesiculosa is a submerged 

 rootless aquatic, which sends only its flowers above the 

 surface of the water. Its leaves resemble those of Dionaea 

 but are much smaller — about a third of an inch long. 

 Sensitive hairs occur on the upper surface, and stimulation 

 of these causes the leaf halves to close together. Glands are 



