270 Mr. D. D. Cunningham. On the Relation of [Xov. 16, 



tional peculiarities in the tissues. The movements in such eases do 

 not necessarily imply the presence of protoplasm specially endowed 

 with sensitive and contractile power proportionate to the magnitude 

 and rate of movement ; they rather appear merely to indicate the 

 degree to which structural arrangements permitting of movement are 

 present. They appear to indicate the degree to which arrangements 

 permitting of massive redistribution of fluids throughout the tissues 

 at large, as distinguished from mere redistribution of cell contents, 

 such as may occur in any tissue composed of closed elements, are 

 present. In other words, the movements may be mere indices to the 

 common sensitive and contractile function of vegetable protoplasm, 

 appearing in dependence on certain structural peculiarities of tissue, 

 and not indices to the presence of specially endowed protoplasm. 



While, however, structural peculiarities of tissue, according to this 

 view, appear to be essential determinants of the occurrence of move- 

 ments, the presence of a contractile and sensitive protoplasm is, of 

 course, necessary in order to the actual occurrence of movement — in 

 order that the apparatus for redistribution of fluid, and consequent 

 redistribution of tension throughout the tissues, shall be called into 

 play. In connexion with this, too, it is important to bear clearly in 

 mind that, while porosity of the tissue elements appears in these 

 cases to be their most important structural feature in relation to the 

 occurrence of movement, an extreme porosity of tissue may coexist 

 with an entire absence of movement even where an active protoplasm 

 is still present. For example, in mature leaves of AJhizzia Lebhek 

 movements are entirely suppressed, although the porosity of tissue 

 remains unimpaired, the abolition of movement being associated with 

 thickening and altered consistence of the cell-walls of the pulvinar 

 parenchyma, increased lignification of the vascular bundles, and 

 excessive cuticularisation of the epidermis. In order to the normal 

 occurrence of movement there must, then, be an active protoplasm, 

 and conditions of structure not merely providing means for ready 

 transfer of fluid, but allowing of ready alterations in the calibre of the 

 tissue elements. In connexion with the subject of concussion move- 

 ments, it is also pointed out that in those cases where a distinct pro- 

 pagation of stimulation from one part to another, as in Mimosa jmdica, 

 occurs, special structural means are present, which may serve as a me- 

 chanical substitute for a nervous conducting apparatus. These means 

 consist of a continuous system of definite air-passages uniting the 

 intercellular spaces of the different contractile organs, and calculated 

 to serve as channels for the propagation of impulses arising from the 

 sudden injection of liquids from the cells of the contractile tissue into 

 the spaces normally occupied by air. 



In regard to nyctitropic movements, it is shown that the parenchyma 

 of the pulvinar organs consists of portions differing from one another 



