IN VEGETABLE BIOLOGY. 201 



Haberlandt's recent discovery of tannic acid, or at least a body 

 very like it, as the osmotically active substance in the sensitive 

 plant, I think one may venture a little further and. suggest 

 that it may be to the glucoside that the peculiarities of lignified 

 walls are due, the tannin performing the same osmotic function 

 in these walls that it does in the cells of the Mimosa. But when 

 occurring in meristem-walls tannin is apparently passing through 

 on its way to idioblasts, or to be excreted, &c, and the tannin of 

 the soft bast, collenchyma, &c. is probably transmigratory also. 



It will be remembered that lignified walls stain green with 

 methyl-green just as does the nucleus. Can this imply the pre- 

 sence in relatively large quantity of an iron-greening tannin in 

 the nucleus ? Such an idea would harmonize with present views 

 of the nucleus as governing the formation of proteid in cells. I 

 throw this out as the merest suggestion, for the similarity in 

 reaction between the nucleus and the wails may well be casual 

 merely, and I do not wish to lay myself open to the charge of 



riding a hobby to death. 



Yet one more suggestion. In studying the Fig the reactions 

 of the latex were carefully attended to, with a result which 

 plainly indicated the presence in it of the substance giving, as I 

 suppose, the proteid reactions in cell-walls, and of the other body 

 (glucoside) found in greatest quantity in the hard bast, but also 

 in the other extra-xylemic tissues. Is it therefore possible that 

 the proteid reactions of the latex may be due to tannin, and not 

 to protein at all ? The only reaction which tells against this is 

 the taking up of carmine; but we have seen this to happen by 

 no means universally. The matter requires further investigation, 

 and the behaviour of the latex of other types seems worthy, from 

 this standpoint, of more detailed examination. 



Summary. 



1. The substance in cell-walls to which their proteid reactions 

 are due is not protein, at least peptonizable piotein, because the 

 reactions come off as well after peptonization as before: neither 

 is it tyrosin, since, after soaking in hydrochloric acid, the proteid 



tests are got just as before. 



2. Krasser's list of bodies reacting like proteids is not ex- 

 haustive, for the three reactions given by cell-walls are also 

 given by a solution of catechu. Moreover, the copper sulphate 



