l64 BOTANY OF THE LIVING PLANT 



on through the elements mentioned: much as a wave of pressure can 



, t £££, a rubber tnbe filled with water. If one observer ^mches 



OU( . ( . I1(1 oi lt a aecond observer can feel the wave at the other end of the tube. 



\. in the Bleep movements of Mimosa, so in the shock movement, changes 



targof in the pulvini are responsible. On simulation the cells of one 



ride of the motor tissue suddenly lose the power to retain the water of their 



rouoles with the result that the water filters out into the intercellular 



.paces and that side oi the pulvinus shrinks. Thus in the mam pulvmus 



iU , ents oo u. at the under side on stimulation, with the result that the 



petiole falls (Fig, 98, II.)- B 



e 



Fig. 99. 



Leaves of Droscra rotundifolia ; enlarged. A, in the receptive state before 

 stimulation. B, after stimulation, viewed from above, with tentacles partly 

 in- urved. (After Darwin.) 



Other striking nastic movements are those of Carnivorous Plants 

 (see also Chapter XII.). In Sundew (Drosera) the spathulate leaves 

 bear numerous radiating tentacles, each terminating in a spherical 



md, which secretes a viscid juice containing protein-splitting 

 enzymes (Fig. 99, A). This acts like bird-lime, detaining any small 

 insect that touches it. The tentacles are sensitive to contact and to 

 the presence of chemical substances, especially those containing 

 nitrogen, such as ammonium salts or proteins. When such stimuli 

 are applied the tentacles, as the result of unequal growth, begin to 

 close inwards, sometimes within a few minutes after application of 

 the stimulus (Fig. 99, B). An insect that is responsible for stimulat- 

 ing the tentacles thus becomes enveloped by them, and undergoes 

 digestion by the enzymic liquid which they secrete. In another 

 native carnivorous plant, the Butterwort (Pinguicula), the presence 

 ts leads to an inrolling of the leaf margins, again tending to 

 envelop the insects, and to hasten their digestion by a secretion 



