Prof.F.Cohn on the Contractile Tissue of Plants. 197 



when a nerve is mechanically, chemically, or electrically injured, 

 and the muscles in relation with it are thrown into activity, this 

 happens not by transmission of the mechanical or other force, 

 but by the calling forth of a motor nerve-force which propagates 

 itself along the nerves. 



On applying flame to a leaflet in the compound leaf of Mimosa 

 pudica, it is not only that particular leaflet that is afi'ected (for 

 if so, it might be fairly attributable to the direct eflFect of the 

 heat); but all the other leaflets, and the entire leaf, including its 

 attachment to the stem, are similarly afi'ected, and collapse ; and 

 what is more, the direction of the propagation of the impulse 

 varies according to the point at which it impinges. Indeed, it 

 is impossible to reduce these movements to the level of mecha- 

 nical results ; and the same holds true when electrical is substi- 

 tuted for mechanical force. 



All such facts and considerations concur in proving that the 

 propagation of external excitation in Mimosa proceeds in the 

 same mode as in animals ; and there is little doubt that the 

 vascular bundles constitute the special tissue adapted for this 

 object, and that the phenomena of contractility depend upon a 

 muscular tissue. 



Though not so perfectly, these properties are also displayed in 

 DioTuea, Drosera, and the stamens of Centaurea. The filaments 

 of the last named contract themselves in their entire length 

 when only one point is touched; and the act of contraction 

 manifests itself by undulatory movements, just as in organic 

 muscle. This fact is best shown by preparing the flower of 

 Centaurea so that the filaments are left by themselves, attached 

 below, but set free above by having the anthers dissevered from 

 them. This done, the filaments curve themselves gently out- 

 wards, and look like the arms of a Hydra extended. In this 

 state any one of the filaments may be irritated (as by the point 

 of a needle), with the effect of inducing a series of movements; 

 these at first being a bending of the fibre towards the side on 

 which it is touched, followed by curvature to the opposite side, 

 and, lastly, by undulatory movements along its entire length. 

 On irritating the five filaments on diff^erent aspects, they are 

 bent about in various directions, curving over and crossing one 

 another. 



So far, however, as observation has extended, it would seem 

 that in Centaurea, Dionaa, and Drosera the power of conduction 

 of external impressions is not located in any one tissue, but 

 equally partaken by all, as is seen in the instance of those lowest 

 animals that are destitute of definite nervous and muscular 

 tissue. 



30. On now collecting the facts that energetic movements 



