RHODODENDRON. 



605 



acids, are usually dissolved and liquified again 

 by the application of alkalies. A few drops, 

 therefore, of a solution of hydrate of potash 

 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, tlie glob- 

 ules were found to have resumed their natural 

 appearance. 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 ai'e composed of a con- 

 glomeration of minute corpuscles similar to those 

 just described; the corpuscles which constitute 

 the muscular 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 the external 

 appearance 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 the nervous system. This 

 hypothesis receives additional strength from the 

 great similarity which exists between the med- 

 ullary substance of the brain of mollusca gaster- 

 opoda, the snail for instance, and the cellular 

 medullary tissue of plants. In pursuit of this 

 idea, Dutrochet made a variety of experiments 

 upon the sensitive plant, the results of which 

 seem to be these. " The principal point of loco- 

 motion, or oimobilify, 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 ascer- 

 tained by some delicate experiments, that the 

 power of movement, or of contraction and 

 expansion, exists in the parynchema and cellular 

 tissue of the swelling, and that the central fibres 

 have no specific action connected with its motion. 

 It also appeared that the energies of this nervous 

 power 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 yet further, the author ascertained that 

 in the motion of the sensitive plant two distinct 

 actions take place ; the one of locomotion, which 

 is the consequence of direct violence offered to 

 the leaves, and which occurs in the swellings 

 already spoken of; the other of nervimotion, 

 which depends upon some stimulus applied to 

 the surface of the leaflets, unaccompanied by 

 actual violence, such as the solar rays concen- 

 trated in the focus of a lens. As in all cases the 

 bending or folding of the leaves evidently takes 



place from one leaf to another with perfect con- 

 tinuity, it may be safely inferred that the invi- 

 sible nervous action takes place in a direct line 

 from the point of original irritation, and that 

 the cause by which this action of nervimotion 

 is produced must be some internal uninternip- 

 ted agency. This was, after much curious 

 investigation, determined by the author to exist 

 neither in the pith, nor in the bark, nor even in 

 the cellular tissue filled with nervous corpuscles, 

 and on which he supposes the locomotion of the 

 swelling at the base of the petioles to depend. 

 It is in the ligneous part of the centi-al system, 

 in certain tubes supplied with nervous corpus- 

 cles, and serving for the transmission of the sap, 

 that Dutrochet believes he has found the true 

 seat of nervimotion, which he attributes to the 

 agency of the sap alone ; while he considers the 

 power of locomotion to depend upon its nervous 

 corpuscles alone." 



The sensitive plants are easily reared and pro- 

 pagated ; some of the species ripen seed, ami 

 others may be increased by cuttings from the 

 points of the young shoots. 



Rhododendron. Natural family rlwduracece; 

 decandria, mmiogt/nia, of Linnaeus. This is a 

 genus of highly prized evergreen shrubs, which, 

 in addition to the beauty of the foliage, bear 

 large and showy flowers. The name is derived 

 from the Greek, rodon, a rose; and dendron, a 

 tree. There are several species, chiefly natives 

 of the northern parts of Europe, and North 

 America. 



The rusty-leaved (ferrugineum), and hairy- 

 leaved (Mrsutum), grow wild in great abundance 

 on the mountains of Switzerland, Austria, Savoy, 

 Piedmont, and Dauphiny. They are found grow- 

 ing at the greatest elevation at which trees will 

 vegetate on those alpine ranges; they afford fuel 

 to the shepherds; grouse are said to feed on them ; 

 the white hares sometimes gnaw the bark in 

 winter; but in general, animals do not seem to 

 relish them, probably from their containing dele- 

 terious juices. The galls of a small cynips, are 

 found frequently on them. 



The Daurian rhododendron is almost solely 

 confined to the sub-alpine mountains of southern 

 Asia, the leaves of which are smooth, naked, 

 and dotted. According to Pallas, it first makes 

 its appearance at the mouth of the river Jenisea, 

 and from the river Uda in the pine woods it is 

 very commonly met with. About Backal it is 

 most abundant, and continues throughout the 

 desert tracts of the Mongols, to Thibet and the 

 North of China; at the lena it becomes more 

 rare, and beyond that it decreases in height, has 

 narrower leaves, and a smaller flower. Another 

 species is found in Kamchatka, growing in 

 marshy mountain hollows; and the Caucasian is 

 a native of the summits of Mount Caucasus, 

 near the range of perpetual congelation. 



