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504 MR. S. LE M. MOOBE's STUDIES 



Marbow 



The material used in this research was taken from a Vegetable- 

 Marrow plant at the fag end of the season ; by this means a plen- 

 tiful supply of callus was ensured, irrespective of any which 

 might be formed by cutting of the stem in pieces and by its pre- 

 servation in alcohol, which, as Fischer * has shown, are methods 

 very apt to increase the amount of " Schlauchkopf " and of callus in 

 the sieve- tubes. Fischer f has described " encyclic/' "ento- 

 cyclic," and " commissural" sieve-tubes in Cucurbita, in addition 

 to those of the vascular bundles ; my observations refer to the 

 latter alone. 



The three chief tests for proteids are the xanthoproteic reaction, 

 depending upon the deep yellow colour produced on boiling with 

 nitric acid and after-addition of ammonia, the red coloration 

 imparted by Millon's reagent upon warming, and the blue or 

 blue-pink by copper sulphate and caustic potash or soda, the 

 latter becoming deeper on boiling. Unless a substance gives 

 all these reactions, it cannot be considered to be a true proteid ; 

 if all three are yielded by it in the typical way, the presumption 

 is that protein is present. 



There is no difficulty whatever in getting the xanthoproteic 

 reaction, if only the precaution be taken of adding an excess of 

 ammonia. The method pursued throughout the research where 

 boiling was necessary was the following : — Sections were mounted 

 in the fluid appropriate to each case; a cover-slip was then 

 put over them, and heat was applied by means of a spirit- 

 lamp. If much of the fluid evaporated before the desired effect 

 was obtained, more was run in, the process being continued as 

 long as was deemed essential. The advantage of this method is 

 that the operator always has his material well in hand, and so 

 can prevent over-boiling — a very important matter, as Nvili after- 

 wards appear. In testing with nitric acid and ammonia, then, it 

 u necessary that the latter be in excess : the effect of boiling is 

 usually to cause some swelling of the callus, but not much ; it 

 frequently happens that the sieve-piercing connecting threads are 

 brought beautifully into view by this means. The colour, which 

 is a well-pronounced yellow, is markedly deeper than that, 



* Ber. d. deutsch. bot. GeselLsck. 1885. 



itaceen,' Berlin, 1884. Abstracted 







In Journ. R. Micros. Soc. 1835, p. 477. I have not seen Fischer's memoir. 



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