MOVEMENTS OF THE PARTS OF PLANTS. 549 



24 hours at 30 R., and the determinate length c". The amount of the 

 greatest prolongation in the humid state was then calculated in decimals 

 of the original lengtli=d". 



a" b" c" d" 



F. 260 259 258-5 0-0058. 



G. A strip was cut from the axis of a fresh, straight, thick shoot of a 

 Stapelia, and its length determined=a'", its width and thickness =b"". 

 It consisted entirely of thin-walled parenchyma cells, consisting of per- 

 fectly developed cellulose. It was fastened to a cork, and thus sus- 

 pended in a glass flask, the bottom of which was covered with chloride 

 of calcium. The length it became, after 24 hours' exposure with a tem- 

 perature fluctuating between 10 and 15 R.=e'", width and thickness 

 =^d'", and the amount of the expansion in the humid state, calculated in 

 the decimal fraction of the original length =e' /x . 



a?" b'" c'" d'" e'" 



G. 189 8 174 3-5 0-086. 



The slight contraction that takes place at first in the thin-walled 

 parenchyma cells, which consist of perfectly developed cellulose, is pro- 

 duced by means of elasticity, to which must be added the insignificant 

 hygroscopical contraction of the membrane, whilst the action only 

 becomes so striking through the falling together of the cells in conse- 

 quence of the desiccation. 



As an instance of the application of these phenomena to the expla- 

 nation of the bursting of capsules, I may cite Iris atomaria. The 

 upper half of the wall of the capsule, which separates itself from the 

 other parts, and retracts, consists of the following layers. At the most 

 external part there is an epidermis of flat, very irregular cells, the walls 

 of which are rather gelatinous and slightly porous ; then follow, towards 

 the interior, several layers of parenchyma cells, which are at first flat, 

 and become gradually somewhat rounder, and the walls of which are 

 also rather gelatinous. The walls of the epidermal cells are moderately 

 thick, the layer of parenchyma lying beneath are joined to the latter, the 

 walls become gradually thinner, and, as it appears, are gradually con- 

 verted into cellulose. Very thin-walled cells, which extend almost from 

 the interior to the exterior, form an internal layer containing many 

 intercellular spaces, into which layer the vascular bundles run. Then 

 follows, almost suddenly separating itself from the former, a very thin 

 layer of cells, which being rather thick- walled, and formed of firm cel- 

 lulose, are about ten times as long as broad, and which laterally, for 

 long intervals, frequently only touch each other, like stellate cells, by 

 means of small processes, and which, arranged in different directions, 

 are yet, on the whole, arranged in such a manner that their longi- 

 tudinal diameter is horizontal. Finally, quite towards the interior, comes 

 the epithelium, consisting of tolerably thick-walled, porous, elongated 

 cells, the longitudinal diameter of which almost invariably forms, with 

 the previous cells, an angle of 25 to 30. The entire wall of the 

 capsule, in a fresh state, is li- to 2 millim. thick. The most internal of 

 these layers, together with the epithelium, can contract only a very little, 

 perhaps enough to enable it to tear the margins of the valves from each 

 other. The external layers, on the other hand, must contract very COD- 

 siderably, both in length and width, as it is owing to this that the valves 



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