832 
MR. W. GARDINER ON THE CONTINUITY OF THE 
by staining the section with methyl violet, and washing with alcohol. The dye 
is then dissolved from everything but the tannin drops. With osmic acid they also 
stain a blue-black and with chromic acid a brown-yellow. The latter reagent, how¬ 
ever, affects the protoplasm as well, and thus does not allow the individual drops to 
be distinguished. 
On treating with Chlor. Zinc Iod. it becomes apparent that the parenchymatous 
cells are freely pitted, each such pit being so little stained as to appear quite trans¬ 
parent, thus presenting a marked contrast to the ordinary deep cellulose blue of the 
rest of the cell-wall. The pits, as a rule, are somewhat shallow and of small diameter 
except in those cells bordering on the vascular bundle, which from their peculiar con¬ 
figuration in consequence of the presence of large intercellular spaces exhibit on their 
walls pits of much larger size (Plate 68, fig. 4). The pits are greater in number on the 
longitudinal than on the transverse walls. The thin pit membrane between two cells 
is, except under very favourable circumstances, extremely difficult to observe in the 
unstained condition. It is perhaps brought out most clearly by staining the proto¬ 
plasm with Hofmann’s blue when the unstained wall will be seen as a thin colourless 
membrane separating the protoplasm of one cell from that of the other. 
Even with the most favourable section there is no indication of the existence of any 
connexion between the protoplasm of neighbouring cells. Deep staining with iodine 
or with Hofmann’s blue shows the outline of the protoplasm to be well defined and 
sharply limited by the cell-wall at all points. 
But if the wall be swollen with sulphuric acid, and after washing stained with 
iodine, methyl-violet and glycerine, or Hofmann’s blue, it will become apparent that a 
definite communication between the cells does exist, and that such communication is 
established by means of the pits (Plate 68, fig. 5). The appearance of a well-prepared 
section is extremely characteristic, reminding one to some extent of a gold chloride pre¬ 
paration of corneal connective-tissue cells. The protoplasm, as it has contracted away 
from the cell-wall, has adhered to the membranes of the pits, at those points in the 
cell-wall where pits are present; and in consequence, the whole section presents the 
appearance of a number of stained and interconnected irregularly-shaped stellate 
masses, for the narrow processes of any one mass unite at their apices with those 
proceeding from the neighbouring masses, thus exhibiting a well-defined reticulate 
arrangement. The reason that the processes proceeding from the masses of two 
contiguous cells are opposite one another obviously depends upon the symmetrical deve* 
lopment of pits on either side of the cell-wall (Plate 68, fig. 3). But that the relation 
between two such processes is of the most intimate character is quite evident from the 
fact that in many instances it appears that an optical continuity exists between them, 
thus establishing a means of communication between cell and cell (Plate 68, fig. 5). 
Successful sections are somewhat difficult to prepare, for if the sulphuric acid does 
not act sufficiently long, the cell-wall is either little or not at all swollen, and when in 
this condition cannot be permeated by the dye, and if the action has been allowed to 
