436 TRANSACTIONS AND TROCEEDINGS OF [Sess. lvi. 



consequently observations cannot be carried on with fresh 

 material, and that preserved in alcohol is equally useless 

 since the tannin is completely dissolved by it. If, however, 

 pieces of bark are allowed to lie in a strong aqueous solution 

 of ferric chloride for some days, the contents of the tannin- 

 sacs become solid, and at the same time assume the well- 

 known blue-black colour of tannate of iron. 



Without entering into the chemistry of the siibject, it 

 seems to me that we have here to do with either a mixture 

 or a compound of tannic acid and albumen, or some allied 

 substance. The foil-owing reactions will, I think, make this 

 clear : — 



Ferric chloride coagulates the whole contents of the sacs, 

 causing them to shrink slightly in the process, and 

 at the same time colours them blue-black. 

 Potassium dichromate has a similar reaction, except that 



the colour is in this case red-brown. 

 Mercuric chloride has the same coagulating effect, 1nit, of 



course, no colour reaction. 

 Dilute nitric acid acts in the same way as mercuric 



chloride. 

 Nessler's reagent does not coagulate the cell contents, but 

 produces in the cells a yellow precipitate due to the 

 tannic acid. 

 Ammonium molybdate dissolved in a solution of am- 

 monium chloride gives in the same way an orange 

 precipitate. 

 These various sul)stances were applied simply by allowing 

 pieces of bark to soak in their acjueous solutions for several 

 days, then sectioning and examining microscopically. 



Note on Baknadesia rosea. V,y John H. Wilson, D.Sc. 



