

538 



STUDIES IN VEGETABLE BIOLOGY. 



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larger than the chlorophyll-cells, one is inclined to ask whether 

 the presence of these idiohlasts may not be connected with the 

 closing movement of the stomata. And, lastly, why may not 

 tannic acid have some general relation to the turgescence of cells? 



Summaky. 



















1. Nessler's test for ammonia is a valuable aid to the botanist 

 in detecting with certainty and rapidity the presence of tannin 

 and tannic acid in plants. Other fluids, having caustic potash for 

 a basis, are also good reagents for tannin. 



2. Two chief kinds of tannin are to be distinguished, according 

 to their behaviour with Nessler's fluid : (a) the iron-blueing tannin 

 strikes brown with the fluid, (6) the iron-greening variety is 

 turned yellow by it. 



3. The yellow substance just mentioned readily diffuses through 

 the cell-wall ; this effect is to be ascribed to the caustic potash, 

 for alkaline solutions, even the weakest, will act in the same way. 

 Here we have a provision, by the aid of rain, dew, and activity of 

 soil-organisms, for the excretion of tannin from the general 

 surface of all plants containing this form of it. 



4. In addition to the functions hitherto ascribed to tannin, 

 Haberlandt's recent discovery with reference to the * water-drop 

 exuding on section from Mimosa pudica, renders it possible that 



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tannic acid may have a more general relation to the turgescence 

 of cells. Moreover, tannin is most likely used up in the lignifi- 

 cation of the cell- wall. 







excretory 





non-diffusible kind when occurring in shed organs, may yet, in 

 view of the fact that tannin can act as a source of carbon to 

 fungi, have some indirect connection, via the nutrition of Sapro- 

 phytes, with the metabolism of green plants. 





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