MIMOSA PUDICA.— THE SENSITIVE PLANT. 
Class XXIII. POLY GAM I A. Order I. MONO G YN I A. 
Natural Order, LEGUMINOSJL — THE PEA TRIBE. 
Stem herbaceous, prickly, with the petioles and peduncles more or less beset with stiff hairs or bristles ; 
leaves somewhat digitately pinnate, with 4 pinnee, each pinna bearing many pairs of linear leaflets. Native 
of Brazil. Flowers red. Legumes glabrous in the middle, but with the margins beset with stiff bristles. 
Superior leaves sometimes the same as the inferior ones. This plant is commonly grown in gardens, under 
the name of the sensitive plant, the leaves falling on the slightest touch. Sensitive plants were not un- 
known to the ancients. Theophrastus speaks of the as growing about Memphis in Egypt, and 
Pliny of the JEschynomene, so called from its contracting the leaves at the approach of the hand. It is thus 
characterised in the flowery poetry of Darwin : — 
“ Weak with nice sense the chaste Mimosa stands, 
From each rude touch withdraws her timid hands ; 
Oft as light clouds o’erpass the summer glade, 
Alarm’d she trembles at the moving shade, 
And feels alive through all her tender form 
The whisper’d murmurs of the gathering storm ; 
Shuts her sweet eye-lids to approaching night, 
And hails with freshen’d charms the rising light.” 
The cause of the well-known motion of the leaves of the sensitive and humble plants has been the 
subject of many ingenious explanations ; but it has not been treated by any botanist with so much in- 
genuity as by Dr. Dutrochet, whose theory we give as explained in the Botanical Register. 
M. Dutrochet states, that having ascertained hot nitric acid to possess the power of separating and 
reducing to its simplest form the whole mass of vegetable tissue, and that the same acid produced other 
effects equally advantageous for the examination of the most obscure parts of vegetable structure, he was 
induced to give his attention to that of Mimosa pudica, in the hope of gaining some evidence respecting the 
cause to which its sensibility is to be ascribed. Beginning with the pith he observed a considerable 
number of minute globules, of a greenish colour, intermingled among the cells, and adhering to them in an 
irregular manner. After attempting to show the probability of these globules having deceived Mirble in 
various points of his analysis of vegetation, and especially in regard to the pores, which that botanist sup- 
poses to exist in the cellular tissue of plants, Dr. Dutrochet proceeds to remark, that the application of hot 
nitric acid to these globules renders them perfectly opaque, whence he concludes that they are in fact minute 
cells, filled with a particular fluid which is subject to become concrete by the application of acids. Now it 
is known that such fluids as are thus altered by acids are usually dissolved and liquefied again by the ap- 
plication of alkalies. A few drops, therefore, of a solution of hydrate of potass were suffered to fall upon a 
portion of the pith on which nitric acid had been acting, and the mixture was exposed to the heat of a 
lamp. Being examined after a few minutes, the globules were found to have resumed their natural appear- 
ance. This curious fact indicated, in the opinion of Dutrochet, a strong and unexpected point of analogy 
between plants and animals. According to the microscopical researches of some modern observers, it has 
been ascertained that all the organs of animals are composed of a conglomeration of minute corpuscles, 
similar to those just described ; the corpuscles which constitute the- muscles are soluble in acids, but those 
which compose the nervous system are insoluble in the same acids, and only soluble in alkalies. Now, as 
the chemical properties and external appearance of the particles scattered among the cellular tissue of 
plants, and constituting the nervous system of animals, are the same, the author is induced to infer, that the 
spherical particles of plants are in fact the scattered elements of their nervous system. This hypothesis 
receives additional strength from the great similarity which exists between the medullary substance of the 
brain of Molusca gasteropoda and the cellular medullary tissue of plants. In pursuit of this idea, Dr. Du- 
trochet made a variety of experiments upon the sensitive plant, the results of which seem to be these : — 
The principal point of locomotion or of mobility exists in the little swelling which is situated at the base of 
the common and partial petioles of the leaves ; this swelling is composed of a very delicate cellular tissue, 
in which is found an immense number of nervous corpuscles ; the axis of the swelling is formed of a little 
fascicle of tubular vessels. It was ascertained by some delicate experiments, that the power of movement, 
or of contraction and expansion, exists in the parenchyma and cellular tissue of the swelling, and that the 
central fibres have no specific action connected with the motion. It also appeared that the energy of the 
nervous powers of the leaf depended wholly upon an abundance of sap, and that a diminution of that fluid 
occasioned an extreme diminution of the sensibility of the leaves. Prosecuting his remarks still further. 
