II* VEGETABLE BIOLOGY. 259 



Further Evidence as to the Presence of Tannin in Cell-walls. 



One rather interesting confirmatory test has come off in the 

 case of lignified walls ; this is the coniferin test (hydrochloric 

 and carbolic acids), coniferin being known by the green colour 

 taken in sunlight by lignified walls treated with these reagents. 

 If sections so treated be left overnight in the mixture of acids, 

 the lignified walls will be stained red in the morning. JNow 

 a solution of catechu gives with these acids a splendid brick- 

 red precipitate. 



A priori, it should be easy to ascertain whether tannin is the 

 cause of the proteid reactions of cell-walls, for we ought to be 

 able, by simply boiling sections in dilute acids, to break up the 

 tannin with formation of glucose, and the reactions should now 

 fail. I have succeeded in this to a certain extent with the hard 

 bast of the Fig, thus proving the peculiar substance in its walls 

 to be a glucoside. The bast-fibres of a section boiled for a 

 minute or so in the acid do not turn red on subsequent treat- 

 ment with iodine after careful washing, nor do they take a rose 

 colour with Schulze's solution, nor a blue with methvl-green 

 under similar circumstances. AVith regard to the special tannin- 

 reactions tho result is less satisfactory, since the effects are 

 marred by the appearance of a grey colour in the hard bast walls 

 during the boiling with the acid. Again, in the meristem walls 

 of Isoe/es it is obviously a glucoside which gives the proteid 

 reactions, for these fail in the case of sections boiled for a few 

 minutes with dilute hydrochloric acid. But when we come to 

 study ordinary lignified walls we are met by the difficulty of a 

 fine red colour appearing in these walls after a short boiling in 

 dilute acid. I am at present unable to say to what this colouring 

 is due ; perhaps to coniferin or catechin, neither of which I have 

 yet been able to procure: pyrocatechin it certainly is not, for no 

 red colour is got on boiling a solution of this body with hydro- 

 chloric acid * On the other hand, I find that on boiling a 

 solution of catechu in dilute hydrochloric acid a fine red colour 

 is very apt to appear in the liquid, although this colour vanishes 

 on shaking the test-tube. I think we have reason to suspect 

 from this that the red colour taken by lignified walls boiled in 

 dilute hydrochloric acid may be a decomposition product of a 

 tannin, but the point requires further examination. 



* It may be noted that pyrocatechin gives not one of the five proteid 

 tions employed in these researches. 



