102 Mr W. Gardiner, On the constitution [Feb. 11, 



the other hand, believe that it is rather allied to protoplasm. As 

 we know from Russow's results, the callus is stained by anilin blue 

 (either Hofmann's blue or water blue). This fact may as I have 

 showed point either to its protoplasmic or its mucilaginous 

 character. But with methylene blue no staining whatever occurs, 

 which not only absolutely negatives the probabilities of its 

 mucilaginous character, but also gives a most valuable confirmation 

 to the results which I have already set forth. The very deep 

 staining of the callus with dilute Kleinenberg's haematoxylin 

 also points to its protoplasmic nature 1 . 



As regards its delicacy, and its power of clearly defining the 

 callus, Russow's 2 mixture of iodine in potassium iodide and 

 chlor. zinc. iod. undoubtedly occupies the first place. Then 

 comes Hofmann's blue and haematoxylin, and lastly the rosolic 

 acid test of Szyszylowicz 3 , the staining characters of which are 

 not nearly so distinct, and its properties, so far as I am aware, 

 can only be observed when the section is mounted in a solution 

 of the reagent ; disappearing entirely when the section is washed 

 in order to mount in water, or what not, so as to obtain the greatest 

 amount of differentiated staining. 



Returning now to the main subject under consideration, we 

 see that the mucilaginous degeneration of the cell- wall is of very 

 frequent occurrence, and that the relative proportion existing 

 between the unaltered cellulose and the mucilage may be very 

 variable. In almost all cases however, as Kirchner 4 showed for 

 example in the mucilage of Quince seeds, a definite residuum 

 of cellulose occurs, which may, as in Tragaganth gum, make itself 

 evident by its reactions with chlor. zinc, iod., or as in cherry 

 gum, cannot (michrochemically at least) be detected. 



We are now in a position to deal with the constitution of the 

 middle lamella. To the earlier botanists this structure was known 

 as the intercellular substance, which appeared to be excreted by 

 the cells, and thus formed the common matrix in which the 

 cells were imbedded ; but at the present time we regard it as 

 consisting of the first formed cell-wall together with one or more 



1 Besides the callus, haematoxylin also stains the refringent granules. The 

 dense protoplasm (slime) of sieve tubes is especially coloured by eosin -which how- 

 ever does not stain the callus. From what occurs in Vitis when examined in the 

 winter and summer condition — the sections being stained with eosin — there seems 

 to be some definite grounds for believing that the callus is formed from the dense 

 protoplasm. "Whether the latter is formed by the coalescence of the refringent 

 granules, must for the present be left an open question. 



2 Eussow, loc. cit., Feb. 17th, 1882. 



3 Szyszylowicz, Osobne. odbicie z Rospran Akad. Umiej. w Krakowie, x. (1882). 

 See Bot. Central, xii. (1882), p. 138. 



4 Kirchner, loc. cit. 



