



J 



534 



MR. S. LE M. MOORE S STUDIES 

















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More useful is a mixture of iron acetate and caustic potash, 



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which rapidly colours tannin a brown-pink. With copper sul- 

 phate and potash also the effect is marred by the presence of a 

 precipitate : the tannin idioblasts of the Primrose are coloured 



straw-yellow by this means, and with copper acetate the action, 

 formation of a greyish precipitate, is uncertain. Nessler's fluid 

 without the mercuric iodide, i. e. caustic potash with potassium 

 iodide, gives, in the few cases in which it has been tried, a quickly- 

 got pale brick-red colour. This is a reagent which ought to be 

 further studied, inasmuch as it is free from an objection to the 

 employment of Nessler's fluid founded upon the poisonous nature 

 of mercuric iodide. Addition of caustic potash to potassium bi- 

 chromate is of no use. A modification of Moll's test, in that iron 

 sulphate was substituted for acetate, turned out satisfactory, at 

 least in the case of the Primrose epiderm, since after overnight 

 action of copper acetate the sulphate threw down a precipitate 

 of iron tannate directly, whereas the acetate did not do so for 

 some ten minutes. 



"What one is inclined to consider a fact of some importance to 

 plants, has come to light in consequence of these experiments 

 with tannin. It has been already mentioned that one form of 

 tannin turns yellow with Nessler's test, and that this yellow fluid 

 diffuses out of the cell. It must be confessed that the meaning 

 of this quite escaped me until I came upon Wiesner's * paper, 

 in which it is stated that alkalies generally will colour the iron- 

 greening tannin a bright yellow. The importance of the diffusi- 

 bility of this alkali-yellowing substance is seen when the constant 

 presence of ammonia in the air and in rain-water is remembered. 

 But it is necessary to inquire whether the minute quantities of 

 ammonia found in the air and in rain-water are sufficient to 

 convert the tannin into a yellow diffusible substance. To answer 

 this question a few experiments have been made with the Ivy; in 

 the course of these it was ascertained that exceedingly weak 

 solutions are capable of acting in the above capacity. Thus a 

 1-per-cent. solution of ordinary " liquor ammonise v of the shops 

 itself a diluted solution — gives a pronounced yellow colour to 

 the hairs, emderm* and fnnrtftmpm+.fll tincm* nf tfi« vnnnorTvv stem, 



.* 





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* Bot. Zeit. 1862. Pfeffer (Ber. d. deutsch. bot Gesell. 1886) has noticed that 

 the tannate formed by action of methyl-blue upon a tanriigerous tissue diffuses 





out into the surrounding medium . 













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