Chap. XIII.] SENSITIVENESS OF FILAMENTS. 235 



ment, and the leaf instantly closed. On another occasion 

 two or three touches of the same kind were necessary before 

 any movement ensued. When we consider how flexible a 

 fine hair is, we may form some idea how slight must be the 

 touch given by the extremity of a piece, 1 inch in length, 

 moved slowly. 



Although these filaments are so sensitive to a momentary 

 and delicate touch, they are far less sensitive than the glands 

 of Drosera to prolonged pressure. Several times I succeeded 

 in placing on the tip of a filament, by the aid of a needle 

 moved with extreme slowness, bits of rather thick human 

 hair, and these did not excite movement, although they were 

 more than ten times as long as those which caused the ten- 

 tacles of Drosera to bend; and although in this latter case 

 they were largely supported by the dense secretion. On the 

 other hand, the glands of Drosera may be struck with a 

 needle or any hard object, once, twice, or even thrice, with 

 considerable force, and no movement ensues. This singular 

 difference in the nature of the sensitiveness of the filaments 

 of Dionsea and of the glands of Drosera evidently stands in 

 relation to the habits of the two plants. If a minute insect 

 alights with its delicate feet on the glands of Drosera, it is 

 caught by the viscid secretion, and the slight, though pro- 

 longed pressure, gives notice of the presence of prey, which 

 is secured by the slow bending of the tentacles. On the 

 other hand, the sensitive filaments of Dionjea are not viscid, 

 and the capture of insects can be assured only by their sen- 

 sitiveness to a momentary touch, followed by the rapid 

 closure of the lobes.^ 



As just stated, the filaments are not glandular, and do 

 not secrete. Nor have they the power of absorption, as may 

 be inferred from drops of a solution of carbonate of am- 

 monia (one part to 146 of water), placed on two filaments, 

 not producing any effect on the contents of their cells, nor 

 causing the lobes to close. When, however, a small portion 

 of a leaf with an attached filament was cut off and immersed 

 in the same solution, the fluid within the basal cells became 



^ [Munk(Relchert and Du Bol8- removed. It l8 remarkable that 



Reymond's ' Archlv.' 187(5, p. 10.">) the ebanee from a damp to a dry 



states that the leaves of his atmosphere should produce this 



plants frequently closeil when eflfect. F. D.] 

 the bell-Jar covering them was 



