August 23, 1877] 



NATURE 



349 



and are illustrated by the rhythmical movements of the which exhibit the phenomena in question, it is seen that 

 small lateral leaflets of the trifoliolate leaf of the Indian I in almost all cases a mass of very succulent parenchyma 

 " telegraph-plant," /?(-j-OT(>rt'///'OT ,',nv''?«c | (small-celled cellular tissue), several layers of cells in 



2. Those apparently spontaneous motions of leaves and thickness, envelopes an axial or central fibro-vascular 

 petals which are due to alternations in the intensity of bundle, or a [few such, bundles running parallel to one 

 lii;ht and heat, and therefore obviously to external causes. ' another, these bundles not being sufficiently lignitied to 

 It is motions of this kind which give rise to the varying be hard, and therefore remaining flexible and extensible, 

 diurnal and nocturnal position of the leaves of some and permitting the upward and downward flexions in 

 plants, and to the closing of certain flowers in the which alone the movement generally consists ; the whole 

 evening or in wet weather. is enveloped by an only feebly developed epidermis. The 



3. Those movements of foliage-leaves, or in certain , best known illustrations of these movements are furnished 

 cases of organs belonging to the flower, which are due to by the two species of" Sensitive Plant," Mimosa pudica 

 sensitiveness to touch or concussion. A familiar example and sensitiva, but are also exhibited by the leaves of 

 of this class of movements is furnished by the well-known several other Mimosas, and of species of Oxalis, Robinia, 



irritability of the leaves of the Sensitive Plant ; and it is 

 to this class that we propose to confine our attention in 

 the present paper. 



Two prelimmary remarks may be made, which are 

 applicable not only to the special class of movements now 



, \?»Vi 



m.!^lh:. 



lM«5^ 



' ^^"j-^ 





Desnianthiis, and Smithiaj by the stamens of several 

 species of Be>-beris and of many Compositse, and by the 

 stigmas of Mimulus, Martynia, Goldfussia, Stylidium, 

 and Megaclinium. The following account of the me- 

 chanical forces which set in motion the phenomena in 

 question is taken mainly from the very laborious re- 

 searches of Pfeffer.' 



The very succulent parenchyma is, when the plant is in 

 active growth, always in a very turgid condition ; i.e., the 

 cells are absorbing sap freely through their permeable 

 cell-walls by endosmotic force ; and in so doing tend to 

 stretch the axial bundle, as well as the epidermis which 

 preients an opposing resistance. The sensitiveness or 

 irritability resides entirely in the parenchyma, either on 

 one or both sides of the fibro-vascular bundle. The irri- 

 tability depends on a two-fold cause : firstly, the paren- 

 chymatous cells are perpetually absorbing water by en- 

 dosmose, and thus placing the cell-walls in a state of 

 tension ; and secondly, a slight impulse im- 

 parted to the sensitive cells causes a portion 

 of the absorbed fluid to be driven out 

 , , through their cell-walls. The cause of the 



'/^/^Jtr— movement itself is believed by Pfeffer to be 

 -' —^•'^'^ this : that at the moment when the turgid 

 cells are giving off water, the elasticity of 

 their tense cell-walls comes into play, causing 

 them to contract in proportion to the 

 amount of water expelled. Inasmuch as this 

 water escapes into the intercellular spaces of 

 the sensitive tissue, and from thence is 

 partially transferred to other non-sensitive 

 portions of the plant, the sensitive tissue 

 decreases in volume, while the non-sensitive 

 portion in some other part of the organ 

 becomes correspondingly expanded, the 

 epidermis of the sensitive portion at the 

 same time contracting from its elasticity. 

 This side therefore becomes concave, the 

 other convex ; and the sensitive organ in 

 consequence bends, carrying with it what- 

 Sensiiive Plant (-W"Mi/!/.vy/r^, D.c. cver Other Organs it may bear, which there- 



fore rise or fall according as the concavity of 

 under discussion, but also to the two others to which we . the curvature is on the upper or under side of the organ, 

 have alluded above. .-Ml these three kinds of movements | Immediately after this has taken place the organ is no 

 are manifested only when the parts in question are per- : longer sensitive, the flaccid cells having too little turgidity 

 feclly mature, and when the peculiarity of their internal 1 to allow of the escape of any more water. But after a 

 structure, which renders the phenomenon possible, is fully | short time they again absorb water ; their turgidity in- 

 developed. In this respect they afford a remarkable contrast creases ; their cell- walls become again stretched or tense; 

 to another class of movements exhibited only when the part ! and the previous sensitive condition, as well as the original 

 of the plant is in active growth, of which we have illustra- j position of the parts, is again restored, 

 tions in the singular phenomena of climbing stems and ten- The following is Sachs' and Pfelfer's description of the 

 drils described in detail by Darwin in his " Movements and anatomy of one of the common Sensitive Plants, Mimosa 

 Habits of Climbing Plants." Another peculiarity common \ pudica. The leaf is bi-pinnate, consisting of a petiole 

 to all the three kmds of movements, and again distin- j Irom 4 to 6 centimetres long, with two pairs of secondary 

 guishing them from the movements of climbmg plants, ] petioles 4 to 5 cm. in length, and on each of these from 

 is that they belong entirely to the foliar or appendicular fifteen to twenty pairs of leaflets 5 to 10 millimetres long 

 organs, i.e., leaves in the wide botanical sense, as includ- and r5 to 2 mm. broad. All these parts are connected 

 foliage-leaves, sepals, petals, stamens, and carpels, with one another by the contractile organs described 



and not in any case to axial structures or stems and 

 branches. 



With regard to the anatomical structure of the parts 



above ; every leaflet is immediately attached to the rachis 

 by such an organ from 0-4 to 06 mm. long, and this 



' Pfeffer, Physiolosl^che UntersMcliOT-jen. T.-IiizV. iS-"!. 



