1884.] of the cell-wall and middle-lamella. 101 



the protoplasm; but also mucilage, and that in the case of my own 

 and Russow's observations, the staining was simply due to the 

 mucilage in question. The whole phenomenon of mucilaginous 

 degeneration leading to the production of the intercellular mucilage, 

 may perhaps be most easily followed in longitudinal sections of 

 the petiole of Aucuba Japonica. In the cells with large intercellular 

 spaces, numerous drops of mucilage, in the form of small papillae 

 may be observed on the outer or free surface of the cell-walls, 

 which are not only distinguished by their microscopical appearance 

 before they aggregate to form a layer, but will like the similar 

 substance in Quince seeds, go blue with iodine, owing to the 

 presence in their structure of a definite hydrated cellulose. 



It may be imagined that in consequence of the facts in connec- 

 tion with the staining of Hofmann's blue that the observations 

 based upon the reactions of this substance lose much of their 

 value, and that from a priori considerations the so-called 

 protoplasmic threads may as well be mucilage as protoplasm. 

 Such however is not the case. For the results as to the proto- 

 plasmic character of the threads do not depend upon the reactions 

 of Hofmann's blue alone, but iodine and chlor. zinc, iod., and the 

 sulphuric and molybolic acid mixture were also employed. More- 

 over it is quite possible to experiment upon walls which both 

 consist entirely of pure cellulose, free from mucilaginous degenera- 

 tion, and in which the middle lamella is not conspicuously 

 developed. Thus in the endosperm cells of Bentinckia Conda- 

 panna and Latania Loddigesii which fulfil both of these conditions, 

 the only staining which occurs, is sharply limited to the protoplasm 

 and to the threads, and the results are entirely confirmed by 

 chlor. zinc iod., the reactions of which, towards protoplasm and 

 mucilage, admit of being clearly distinguished. Lastly, all doubt 

 upon the subject is put an end to by the use of methylene blue. 

 This substance, as I have pointed out, stains markedly the cell- 

 walls and all the substances produced by the degeneration of the 

 same, such as mucilage, &c. On the other hand methylene blue does 

 not (unless the staining be forced) colour the protoplasm. So that 

 whereas Hofmann's blue stains protoplasm and mucilage, but not 

 cell- wall ; methylene blue stains cell-wall and mucilage but not 

 protoplasm, and in this way the two may be clearly separated. 



If this be so, it will then be of interest to observe the staining 

 effects of these two reagents upon the callus of sieve-tubes. As 

 regards this substance Janczewski 1 maintains that it is pre- 

 eminently of a mucilaginous nature, while Russow 2 and myself 3 on 



1 Janczewski, Mem. de la Soc. ties Sciences Naturelles et 3Iathematiques de Cher- 

 bourg, t. xxiii. p. 209. 



2 Bussow, Sitzber. der Dorpater Naturfors. Gesell. Feb. 17th, 1882. 



3 Gardiner (loc. cit.). See also Phil. Trans. Part in. 1883. 



