346 BIOLOGY. [Book v. 



Lindsay, Dutrochet, and, after them, many other observers 

 have proved that the principal agent in the movements of the 

 sensitive plant is the bourrelet at the base of the petiole. Ac- 

 cording to Dutrochet, this bourrelet acts as if it were composed of 

 two springs, an tipper and a lower. The first lowers the petiole, 

 the second raises it again. The action of the bourrelet would 

 coincide with its distension, its turgescence, and would be due, 

 according to certain botanists, to an afflux of sap. But how is 

 this afflux of sap produced? How can the movement of the 

 f olioles be explained ? Above all, how can we comprehend that 

 an excitation may be transmitted from one leaf to another, some- 

 times even to a distant leaf, missing the nearer leaves, sometimes 

 across the entire plant, since all the leaves contract successively, 

 when a drop of sulphuric acid is sprinkled upon the roots.' 



We must admit here the intervention of the anatomical ele- 

 ments of contractile tissues, analogous to those which exist in 

 animals. In effect, M. Vulpian has found, at the junctions of 

 the folioles, and at the base of the petioles, cells containing a 

 finely granulated jelly, which he compares to the substance of 

 muscular fibres, and which he says he has seen contract under 

 various excitive influences. M. Cohn, of Breslau, has found 

 analogous histological elements in the filaments of the anthers 

 of the cynarese ; that is to say, elongated cells, longitudinally 

 striated when at rest, contracting under the influence of various 

 excitants, and then presenting transverse strise, of a very vivid 

 kind. 



These anatomical elements may possibly be the. agents of the 

 local movements, directly provoked. As to the indirect move- 

 ments, transmitted to leaves non-excited, we cannot account 

 for them without admitting a certain contractility of the sap 

 vessels, along which the stimulus is transmitted from one to 

 the next. This kind, of vascular contractility is rather animal 



^ Vulpian, Lsfons sur la Physiologie Gomparie du Systime Nerveux, p. 

 31, 32. 



