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IN VEGETABLE BIOLOGY. 



503 



















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A third view has recently been propounded by Eendle *, who, 

 by a thorough examination of the Onion, believes the callus in 

 tins plant to owe its existence partly to the wall, partly to the 



protoplasm. 



It ' 

 t is necessary to give this brief historical resume, because, as 



will hereafter appear, some of the facts brought forward in the 

 present memoir are, it is believed, of such a nature as to put an 

 end, once and for all, to the conflict in opinion which has prevailed 

 upon the origin of callus, so far at least as regards the two types 

 here dealt with. 



With reference to the other matter, viz. the nature of callus, 

 we find De Bary f noting the yellow colour it takes with iodine 

 dissolved in potassium iodide, its swelling in hydric sulphate till 

 Its outline is completely lost, and its swelling up in caustic 

 potash. Russow J appears to have been the first to hazard an 

 opinion as to the chemical constitution of callus: having hit 

 upon the method of staining it with aniline-blue, and also with 

 that mixture of iodine and Schulze's solution now known as 

 •Russow's reagent, he remarks § that it is proteids, and especially 

 auclein, that eallus most closely resembles. Unfortunately, just 

 at this time Szyszylowicz || discovered the brilliant colour takeu 

 by callus in corallin-soda— a fact which set observers upon a wrong 

 tack altogether. It was assumed that because starch and muci- 

 lage both take up corallin-soda, because the protoplasm of the 

 sieve-tubes uudergoes, after the disappearance of the nucleus, a 

 change into slimy matter, and because this change is accompanied 

 by solution of the starch, for these reasons it was assumed that 

 callus is a sort of starchy mucilage. This idea is, at least as far 

 as the facts hereafter brought forward go, a wholly incorrect 

 °ne ; and I will now proceed to defend this statement. 











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Ann. of Uot. vol. iii. 



i" Vergl. Anat. Engl. Trans, p. 175. 



t Sitzb. der Dorpat. naturforsch. Gesellscb. 1881. 



§ L. c. (1882 memoir). 



II Vide Janczewski, I. c. (Note Additionelle). Also a Polish memoir by 

 %szylowicz, wbicb I have not seen, but which is abstracted in Bot. Central- 

 Watt, Band xii. p. 138. 



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