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In the epiderm 







scattered 





IN VEGETABLE BIOLOGY. 537 



of the Primrose we find tannin idioblasts 

 e chlorophyll-containing cells, and we hare 

 already seen how, in earlier states of the leaf's development, 

 these idioblasts are only distinguishable from the cells among 

 which they lie by their containing fewer chlorophyll corpuscles, 

 although even now they have much tannin. "What is it which 

 determines whether a cell shall become an idioblast or remain a 

 chlorophyll cell ? What happens is probablv this :— One con- 







tannin 









tannin is passed on from cell to cell either by diffusion through 

 the wall or by active movements of the connected protoplasts 

 Ihe cells, then, besides manufacturing tannin, are continually 

 receiving it from other cells and passing it on ; the tannin-streamsf 

 will thus obviously tend to converge towards certain points, and 

 at these points tannin will accumulate. Accumulation of tannin 

 is unfavourable to metabolism, and after a time the cell will de- 

 generate to a mere passive recipient of tannin from other cells. 

 •But there must also be lateral movement in the epiderm to the 

 idioblasts overlying the vascular bundles, for there is almost always 

 niore tannin in these idioblasts than in those situated in other 

 parts of the epiderm L and it is this evident movement of tannin 

 towards the conducting tissues which would seem to argue for it 



is of 



than a merely excretorv role. Whether 



plant 



all 









clear. Of course it may preserve the leaf from the attacks of 

 injurious animals (insects &c.),- but when one recalls Haberlandt's 

 recent discovery relative to tannin (or rather tannic acid) as 

 being the osmotically active substance in Mimosa pudica, and 

 connects with it the fact that the tannin-idioblasts of the Primrose 

 are almost always after a time somewhat, and often markedly 



Either method is possible ; for on the one hand Vesque (' Comptes Rendus,' 

 !886 ; abstr. Journ. R. Micros. Soc. 1887) 



ease from one epidermal cell to another ; and continuity of protoplasm is often 

 *o be seen with exceptional clearness in the epiderm {e.g. Schaarschmidt, Magy. 

 N6V.. Lapok, 1884, abstr. Journ. R. Micros. Soc. 1885 ; and Tangl, Siteb. d. k. k. 



-Akad. Wise. Wien, 1884). _. 



t That there are such streams is proved by the existence of the so-called 



tannin -bridges (vide Moeller, Ber. d. Deutsch. bot. Gesell. 1888). 



X This point was enunciated in the writer's second memoir on - L Ig ht and 

 Protoplasm - (Journ. Linn. Soc., Bot. xxir. p. 377). Some months after the 

 ng, but a little while before the publication of that memotr, Moeller (I. e.) 



pass 



made 



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WNN. JOURN.— BOTANT, VOL. XXVII 2 p 







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