CHAP. XVI. 



MOVEMENTS OF THE LEAVES. 



S71 



doubt that it profits by its power of digesting and 

 absorbing matter from the prey which it habitually cap- 

 tures in such large numbers. It will, however, be con- 

 venient first to describe the movements of the leaves. 



Movements of the Leaves. That such thick, large leaves 

 as those of Pinguicula vulgaris should have the power 

 of curving inwards when excited has never even been 

 suspected. It is necessary to select for experiment 

 leaves with their glands secreting freely, and which 

 have been prevented from capturing many insects ; as 

 old leaves, at least those growing in a state of nature, 

 have their margins already curled so much inwards 

 that they exhibit little power of movement, or move 

 very slowly. 1 will first give in detail the more 

 important experiments which were tried, and then 

 make some concluding remarks. 



Experiment 1. A young and almost upright leaf was selected, 

 with its two lateral edges equally and very slightly incurved. 

 A. row of small flies was placed along one 

 margin. When looked at next day, after 

 15 hrs., this margin, but not the other, was 

 found folded inwards, like the helix of the 

 human ear, to the breadth of -^ of an 

 inch, so as to lie partly over the row of 

 flies (fig. 15). The glands on which the 

 flies rested, as well as those on the over- 

 lapping margin which had been brought 

 into contact with the flies, were all secreting 

 copiously. 



Experiment 2. A row of flies was placed 

 on one margin of a rather old leaf, which 

 lay flat on the ground; and in this case 

 the margin, after the same interval as be- 

 fore, namely 15 hrs., had only just begun 

 to curl inwards; but so much secretion 

 had been poured forth that the spoon- 

 shaped tip of the leaf was filled with it. row of small flies. 



Experiment 3. Fragments of a large fly were placed close to 

 the apex of a vigorous leaf, as well as along half one margin. 



Fl " lr> - 



