EXTRACTS FROM FOREIGN PERIODICALS. 200 



tenuity, and intermixed with globules disposed in longitudinal series. A blade 

 raised longitudinally upon this fibrous tissue being plunged into aerated water, 

 directed its curvature towards the centre of the petiole ; if this blade be placed 

 in non-aerated water, it will not curve at all. Thus this fibrous tissue is 

 incurvable by oxygenation ; under this is found a woody substance with medul- 

 lary rays, and principally composed of sap-vessels and of a considerable quantity 

 of large pneumatic tubes. In the centre of the petiole there is a bundle of fibrous 

 tissue similar to that described above, and taking the place of the pith in this 

 petiole which represents a little stalk. When this is exposed, we find that the 

 petiolary bending of the leaflet of the Kidney-bean contains the two incurvable 

 tissues which I have already described in flowers capable of closing after expansion, 

 namely, the cellular tissue incurvable by endosmose, and the fibrous tissue in- 

 curvable by oxygenation. The two cylindrical layers inclosed one in the other 

 which form these two tissues, would be represented sufficiently accurately by 

 the reunion and attachment in a cylindrical bundle of a certain number of nerves 

 of the flower of Mirabilis. I have pointed out, that near these nerves the 

 cellular tissue curves outwards by endosmose, and that the fibrous tissue curves 

 inwardly by oxygenation ; which produces in the first case their state of expan- 

 sion, and in the second that of sleep. The same would happen in the petiolary 

 curvature of the leaflet of the Kidney-bean, if we suppose that the two 

 cylindrical layers, the one exterior to the cellular tissue, the other interior to the 

 fibrous tissue, are divided at the same time into fine longitudinal bundles. Each 

 of these bundles is analogous to a nerve of the flower of Mirabilis ; there will be 

 in it, and arranged in this nerve, the two incurvable tissues capable of effecting 

 the expansion and the closing. Supposing these bundles reunited by a mem- 

 branous tissue, that would form a corolla susceptible, by turns, of expansion and 

 closing, or of waking and sleeping. But this state of separation of longitu- 

 dinal fasciae does not exist in the petiolary curvature ; these fictitious fascia? 

 are intimately united, and form a hollow cylinder composed of two layers ; 

 the cylindrical layer of fibrous tissue is inclosed in the cylindrical layer of 

 cellular tissue. Let us suppose each of these cylindrical layers divided into 

 longitudinal threads, joined to each other. The longitudinal threads of cellular 

 tissue would dispose all to direct their curvature outwards. Now it is evident, 

 that if their power of incurvation is equal, the cylindrical layer which they 

 form by their junction will remain straight and equal ; but if the longitudinal 

 threads of one side of the cylinder force it by the power of incurvation to] the 

 threads of the opposite side, these would be impelled in the direction of incurva- 

 tion effected by the threads which antagonise them. The same reasoning may 

 be employed in relation to the cylindrical layer of fibrous tissue subjacent to 

 the cylindrical layer of cellular tissue ; thus each of these cylindrical layers 

 vol. in. — no. xix. 2 r 



