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508 MR. S. LB M. MOO RE'S STUDIES 



upon treatment with iodine surround threads of slime, and, 

 according to Fischer, this is due to conversion of the slime into 

 callus, the process taking place from without inwards. In addi- 

 tion to this, it has always heen a stumbling-block in the way of 

 adherents to the other theory, that the sieve-plates of many 

 perennial plants are cleared in the spring. This one cannot 

 understand as happening if the callus be merely transformed 

 sieve-plate; and, besides this, as already mentioned, Fischer finds 

 an increase in the amount of "Schleimkopf " and callus from 

 mechanical injury and from preservation in alcohol, which is expli- 

 cable on the deposition theory alone *. However, although, in my 

 opinion, the latter theory has always been the stronger, the battle 

 between the two views has necessarily been a drawn one, because 

 continuous observation of a sieve-plate was impossible. But in 

 the new method of employing a peptonizing fluid we have the 

 means of keeping under observation one and the same sieve-plate, 

 which we can see gradually clearing, and, finally, quite free from 

 callus. We can then examine a sieve-plate which but a few hours 

 previously was obliterated with callus, and find it in exactly the 

 same condition as before callus made its appearance upon it. 

 And when we remember that the callus is, at least in the 

 Vegetable-Marrow, undoubtedly a proteid, and, as such, cannot 

 possibly be formed from cellulose, it is submitted that the question 

 is definitively settled, so far as the Vegetable-Marrow is con- 

 cerned. 



With what class of proteids should Vegetable-Marrow callus be 

 assorted ? To answer this question, it is necessary to know its 

 behaviour to neutral saline solutions: those employed in this 

 research were sodium chloride and potassium nitrate, in each 

 case in 1 per cent., 10 per cent., and saturated solutions. In no 

 case did the callus betray any tendency to dissolve. From its 

 insolubility in water and in neutral saline solutions, as well as in 

 dilute acids and alkalies, while it dissolves in strong hydric sul- 

 phate, and, to some extent at least, in caustic potash, Vegetable- 

 Marrow callus recalls, and may perhaps be classified with, the 

 Coagulated Proteids. 





* Here, too, one may mention Janczewski's observation, that sometimes the 



ive-t.ii}v».a rvf r\\A iiliiiAmAa **i? r>z^.«^ M .^» ^« * u~—« 4-Ks>;« uinwc nnen in 



•tubes of old rhizome 











, 



winter. This is supposed by Janczewski to be due to the tubes no longer con 

 taining protoplasm. But why should disappearance of the protoplasm prevent 

 formation of callus, if mere swellhur-UD of the wall is involved ? 











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