

IN VEGETABLE BIOLOGY. 237 



perature of the body. We see how the callus lias disappeared, 

 leaving the sieve quite clear, leaving also in position the thin 

 film of Schleimkopf which was closely apposed to the callus- 

 mass. Fig. 5 shows what occurs in the Fig : here there was no 

 film of Schleimkopf, and all one sees is the perfectly cleared sieve. 

 Moreover, as showing the identity between Vegetable-Marrow 

 callus and that of the Fig and Ash, it was found that the former 

 substance also dissolves in gum-arabic. By this treatment one 

 can get beautiful preparations showing cleared sieves with slime- 

 threads passing through the pores, and so connecting the proto- 

 plasts : this is shown by fig. 6, where the sieve is seen free from 

 callus, the Schleimkopf (s) — a large mass on one side, and greatly 

 reduced on the other — remaining with the same contour that it 

 had when callus was present, and the connecting-threads, around 

 which the callus was deposited, remaining in their original posi- 

 tion. These facts may be commended to anyone who favours 

 the swelling-up theory of callus-formation, a theory which they 

 seem emphatically to contradict. 



Search for a CaUolytic Ferment. 



How is callus dissolved away from the sieve-plates ? Most 

 probably in one of two ways, either by means of a ferment or 

 of an acid or alkali — possibly by cooperation of ferment with acid 

 or alkali. I regret being unable, after spending some months 

 upon this question, to give it a definite answer ; and the case 

 being thus, I shall not go into my various experiments in detail. 

 If there be a callolytic ferment in gum-arabic, it must act in 

 presence of an acid, for a solution of the gum has a decided, 

 though not a very strong, acid reaction. "Working with gum- 

 arabic solution, I tried the precipitation method of ferment-isola- 

 tion, but without any success ; and the same failure followed all 

 the experiments with glycerine extracts of crushed gum. The soft 

 bast of the Ash gives a feebly acid reaction— at least in early spring ; 

 and this seems to indicate that the contents of the sieve-tubes 



are acid. With 



preci- 



pitation and glycerine-extract ; but all was labour in vain. But 

 I have not yet tried with gum-arabic the method of dialysis, 

 which may possibly bring success in its train. 



