210 EXTRACTS PROM FOREIGN PERIODICALS. 



of incurvable tissues acts in this case as if the only side of the cylinder 

 whose force predominates alone existed in each of them. The opposite side 

 of the cylinder, whose antagonising power of incurvation is overcome, would 

 only act here as a moderator of the action ; it is precisely what happens. — 

 Experience has convinced me that in leaves, as in flowers, the tissue incurvable 

 by endosmose is the sole agent of the expansion, and that the tissue incurvable 

 by oxygenation is the exclusive agent of sleep. 



These two incurvable tissues, arranged, as I have described, in two cylindrical 

 layers inclosed one within the other, doubtless act throughout the mass of the 

 cylindrical layer or of the hollow cylinder which they form. But only the 

 strongest of each of these hollow cylinders manifests its action exteriorly, and 

 that by the excess of its force on that of the other sides of the same hollow 

 cylinder. I have observed that the expansion of leaves always takes place by 

 the action of the strongest part of the cellular tissue of the petiolary curvature. 

 Hence this cellular tissue incurvable by endosmose is the undoubted agent of the 

 expansion of leaves. Their sleep is certainly owing to the sole action of the 

 fibrous tissue incurvable by oxygenation, contained in the same petiolary curva- 

 tures, for I have ascertained that by depriving leaves of respiratory oxygen their 

 sleep is prevented ; they remain always expanded, as I have also proved to be 

 the case as regards flowers. Then the fibrous tissue incurvable by oxygenation, 

 and the unassisted agent of sleep, is paralysed. 



The phenomena of the expansion and closing of leaves, at first sight ap- 

 parently very] complicated, are thus subject to the simple laws which cause the 

 sleeping and waking of flowers. 



The petiolary curvatures of the leaflets of Robim la pseudo-acacia, and the leaf 

 of the Licorice {Glycyrhiza glabra) present sufficiently accurately the same 

 organization as that described in the Kidney-bean. The petiolary curvature 

 situated at the base of the petiole of the Sensitive-plant (Mimosa pudica, Linn.) 

 is different. Its fibrous tissue, the agent of sleep, directs its concavity towards 

 the centre of the petiole, which takes place in the same manner as in the other 

 plants mentioned. But, contrary to what happens in these same plants, its 

 cellular tissue, the agent of expansion, directs the concavity of its curvature 

 towards the centre of the petiole, like the fibrous tissue. Since expansion is a 

 straightening action, as in the leaves of the plants alluded to, there should be, in 

 the petiolary curvature of the Sensitive-plant, an inversion in the position of the 

 predominant side of its cellular tissue, the agent of expansion ; this is also what 

 takes place. 



This fibrous tissue, incurvable by oxygenation, being, in the Sensitive as in 

 other plants, the agent of sleep, and the incurvation of sleep being in it the same 

 as the incurvation taken under the influence of stimulants, it follows that it is 



