

















































s 



IN VEGETABLE BIOLOGY. 533 



but further information on this subject can scarcely be expected 

 from a botanist. 



A few words now, before proceeding to speak of some other 

 tannm-reactions, about the " glucoside or glucoside-like sub- 

 stance " recently found by Haberlandt * in the drops of fluid 

 exuding from cut surfaces of Mimosa pudica, and called by former 

 authors « water-drops." This substance is met with in certain 

 large elements scattered through the leptoni, which Haberlandt 

 believes is the path taken in the conduction of a stimulus from 

 part of the plant to another ; it is strongly acid, and is held by 

 -Haberlandt, and apparently with reason, to be the substance by 

 whose osmotic activity is brought about the relatively high degree 

 oi turgescence the abolition of which on sectioning results in 

 exudation of the drop. With iron salts a purple colour is taken 

 °y it, as Haberlandt shows, and, on heating with acids, a body- 

 reducing copper oxide is formed. 



one 



Hab 



have 



that not only is the body in question a glucoside, but that it is 

 tannin or tannic acid. Thus ammonium molybdate gives a decided 

 yellow, and potassium bichromate a brown colour to the crystals 



which 



drop 



which is a very pretty sight. Nessler's fluid is less satisfactory : 

 a well-marked yellow solution is obtained with it, and a slight 

 brown residue which has to be carefully looked for. It is neces- 

 sary, in applying these reagents, to use them in very small quan- 

 tities, otherwise the result sought for will not be reached ; so, 



too 



that the purpling occurs. 



tannin 



It 



rule 



potash to a tannin-reagent quickens its action. Thus if it rein- 

 forces ammonium molybdate an immediate, though faint yellow 

 colour is given to the idioblasts of the Primrose and to the sub- 

 sidiary cells of Grevillea robusta. But inasmuch as caustic 

 potash alone will produce a closely similar effect, it is not certain 

 whether the molybdate cooperates in this. "With caustic potash 

 and iron sulphate an almost immediate purple or purple-black 

 preeimtfl.** ,* a fi,™«r„ a**™ \r> f.fcA <>a118 of the Primrose : but all 









un 



account of the precipitate caused by their coming in contact. 



JZ ST 





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Reizleitende Gewebesyatem der Sinnpflanze,' Leipsig, 1890. Jgj., /{,, /jf 









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