IN THE MOTOR ORGANS OF LEAVES. 



3 



established. Whore conditions favouring the formation of cndosmotic products by the 

 protoplasts are present coincidently with conditions implying abundant general supply and 

 small general loss, and in the absence of any special causes for active local nitration, 

 turgescence will naturally attain its maximum; where active formation of endosmotic 

 materials coincides with conditions causing deficient supply or excessive loss of fluid, the 

 result in any individual case will be determined by the degree to which each of the 

 opposed sets of factors happens to prevail; and, where a small formation of cndosmotic 

 materials and conditions favouring loss or obstructing supply of fluid occur coincidently, 

 minimal degrees of turgescence will naturally present themselves. 



.~~~ ~~ *"--© 



The variations in turgescence due to the interaction of these various factors mu 

 ssarily give rise to various ultimate results according to the nature of the tissue 

 which they occur. In the cases of 



conditions for the 



occurrence 



of natural plasmolysis occur, varying degrees of contact or separation between the 

 protoplasts and the cell-walls will be present, which may be accompanied by conspicuous 

 alterations in colour, especially where the protoplasts include coloured contents. In other 

 cases varying degrees of intracellular pressure will coi >tantly prevail which may or 



be accompanied by corresponding variations in bulk of the tisane. Where the 

 walls are rigid, either intrinsically or from their relations to neighbouring pnrts, 

 ations in intracellular pressure alone will be present; where tliey are extensile and free 



variations in size will accompany this. It is only in the latter case that varia- 



a y 



to extend, variations in size 

 tions in decree of turgidity can give rise to conspicuous massive movement., and it does 

 not of course, follow that such should invariably present themselves even under such 

 conditions. Variations in the size of the constituent elements of a tissue may result in 

 mere general increase or decrease of its bulk, and it is only where variations in turgidity 

 affect opposed masses of tissue in unlike degree that massive movements will accompany 



them. 



Mere variations in protoplastic turgidity may give rise to very conspicuous changes 



in the colour of masses of tissue; variations in the turgidity of the tissue elements as 

 a whole in cases where the cell-walls are rigid, may cause appreciable variation in consist- 

 but cannot serve to induce appreciable variations in bulk or massive movements; 

 variations in turgidity of entire tissues with extensile and elastic cell-walls will cause 

 variations in bulk which may or may not be accompanied by conspicuous movements 



according to their distribution. 



Fluctuations in turgidity are then, under certain circumstances, efficient in giving 

 rise to massive movements in vegetable organisms, and may themselves be caused either 

 by variations in the nature and amount of the products of protoplastic activity, or in 

 conditions of supply and loss of fluid ; and the question next arises, are they the only 



ence 



efficient agents in producing this result, or may 



of contractile funct 



_. be one also, as, according to ordinarily accepted opinion, it may actually be? 



So far as protoplasts are concerned, it is readily conceivable that active contraction 

 may determine alterations in turgescence, and therefore in bulk, by causing the 

 discharge of fluids included within their substance; but the question which we have to 

 deal with is, how far is mere protoplastic contraction likely to be efficient in giving rise 

 to alterations in the turgescence of cells ? In considering this we have in the first place 

 to bear in mind that, in so far as the active protoplasm is concerned, we have unequivocal 

 evidence that contraction does not imply any appreciable alteration in bulk, but mere 

 change in form, and that therefore contraction of a protoplast situated within a cell cavity 



Ann. Roy. Bot. Card. Calcutta Vol. VI. 



