MR. W. GARDINER ON THE CONTINUITY OE THE 
8‘2 8 
in two adjoining cells * any unequal thickening that may occur always takes place 
symmetrically on either side of the first formed cell-wall, and in such a way that the 
two pits which are formed in consequence are exactly opposite one another. 
Among many other examples, the thickened cells of hard endosperms and the paren¬ 
chymatous tissue of all pulvini exhibit this structure to a high degree, and since it 
was probable that by means of these pits a communication between adjacent cells was 
established, the study of the nature of the pit-membrane becomes one of great import¬ 
ance. The result of experiments with various staining reagents may now be detailed. 
As at first mentioned, Chlor. Zinc Iod. usually stains the pit membrane but little.t 
Instead of treating the section with this reagent alone, better and more decisive 
results may be obtained by first soaking the tissue in iodine, then rapidly washing to 
get rid of the extraneous iodine which would otherwise be precipitated over the tissue, 
and then mounting in Chlor. Zinc lod., or the section may be first treated with Chlor. 
Zinc Iod., then washed and mounted in iodine solution. This gives good results in 
cases where protoplasm is left sticking to the pits as in the parenchyma cells of the 
pulvinus of Amicia or the endosperm cells of Bomarea. 
Methyl violet gives very striking, and at the same time is apt to give very decep¬ 
tive results. When a washed out section of pitted tissue that has been exposed to the 
action of sulphuric acid is treated with this reagent the whole of the tissue becomes 
rapidly stained. The protoplasm is coloured a deep purple ; the cell-wall is stained 
violet; and the closing membrane and sides of the pit are brought into prominence 
since they assume a purple colour, somewhat lighter than that of the protoplasm. The 
middle lamella also stains deeply. Now in a much-pitted tissue, e.g., that of a pul¬ 
vinus, the cell wall after treatment with sulphuric acid usually becomes much swollen, 
causing an elongation and at the same time a narrowing of the pits, and may, more¬ 
over, in its swollen condition closely invest and surround the protoplasm. When such 
a section is treated with methyl violet, the deeply stained tubular pits, being placed 
symmetrically opposite one another on either side of the common cell wall, abut on 
the shrunken and similarly stained protoplasm, and give the impression that a distinct 
and well-defined continuity exists from cell to cell. Thus in Amicia the most beautiful 
and striking appearance is produced which is further heightened by the fact that pro¬ 
cesses from the main protoplasmic mass usually go for some distance into the pits. 
(See Plate 68, fig. 10.) If, however, the section be treated for some time with dilute 
glycerine, the colour is dissolved from the cell wall and the pits and the protoplasm 
alone remains stained, thus making the real state of things apparent. 
The reaction with methylene blue is perhaps the most characteristic. When a 
section is stained with this reagent before treatment with sulphuric acid, the cell 
wall and the pit membrane will be deeply coloured, the protoplasm being left unstained. 
* I exclude from this statement such cases as that of a cell adjoining a vessel, &c. See ‘ Sach’s Text¬ 
book,’ English edition, 1882, p. 26. 
f In old cells with thick pit membranes the staining of Chlor. Zinc Iod. is, however, A T ery apparent. 
