THE VEGETABLE CELL. 151 



fact. For, mucK as Kas been written concerning the sleep of plants, 

 notMng wliatevez' is yet made out of the manner in -wbich light acts upon 

 the cellular tissue, whether, as Treviranus assumes {^^ Physiologle!^ ii, 750), 

 the activity of the latter is excited by light in consequence of an irri- 

 tabihty of the cellular tissue ; or, as Dutrochet thought (" Memoires,'' i. 

 525), the excretion of oxygen occurring under the influence of light 

 brings about an increased ascent of sap, and a consequent turgescence of 

 the cellular tissue, or, on the contrary, according to Dassen s hypothesis, 

 superabundance of crude sap produces the nightly sleep ; or whether, as 

 Macaire supposed, the absorption of carbon, combined with excretion of 

 oxygen, occurring under the influence of light, is to be regarded as the 

 cau'^e of the movement. In particular the variations in the movements 

 of leaves, some of which sink down while others rise up in sleep, hire 

 not yet been traced back by anatomical research to any deflnite difference 

 of organization. It is true Dutrochet {'^ Memoires" i. 469) took much 

 pains in endeavouring to make out the cause of motion through anatomi- 

 cal investigation of stems and leaves, whereby he arrived at results similar 

 to those in his above-mentioned investigation of the axial organs, since he 

 thousrht he found, besides the curvable cellular tissue, a curvature of the 

 you4 fibrous tissue produced by aDsorption of oxygen ; but a minute 

 exposition of his views appears to me to be superfluous. The complaint 

 has been made, in other quarters, of the work of Dutrochet, that it is 

 incomprehensible. I would not complain of this so much, as that the 

 illogical conclusions of the author, and the arbitrary style in which he 

 introduces unfounded statements of facts (with wiiich I have already 

 found fault above), have increased in proportion with the complicafcion of 

 the phenomena which were to be explained. A wide but d&cult field 

 stm lies open here to the experitnental physiologist. 



Besides the movements already described independent of ex- 

 ternal material influences, peculiar motions of particular organs 

 are met with in a number of plants, ensuing only through the 

 action of stimuli accidentally effecting them, -whence a sensitive- 

 ness or irritability has been ascribed, to these plants. 



Ohserv. We meet with such phenomena of irritability in the leaves of 

 a not very large number of plants of the families of Leguminosse, Oxar- 

 lidese and Droseracese. Among the Leguminosae, it is principally in plants 

 of the genus Mimosa^ of which M, pudicdj above all, has been the sub- 

 ject of minute investigation j besides these, there are the various species 

 of liohinia, and some species of JBschynomene, J^mithia and Desmanthus ; 

 in the family of the Oxalidese probably all the plants possess more or lese 

 distinct traces of irritabihty, but only the pin|iate-leaved Biophytmn semf 

 sitwmn in a high degree ; among the Droseraoeaa, tlie leaves of Diono&q, 

 muscipula have a most remarkable irritability, while our indigenous spe- 

 cies of Brosera only exhibit traces of it. 



In my opinion, a duU irritability exists in the stems of twining plants, 

 and tendrils. 



The same property is exhibited also by the stamens of species of Ber- 

 heris and Mahofda, by Spa^mcmnior aJHmTmj of many species of Gmtus^ 

 Cistiis, of many phintfo of the section Cynaroceplndm ; moreover by the 



