834 
MR. W. GARDINER ON THE CONTINUITY OF THE 
expect such physiological differences to be made apparent by a somewhat coarse 
histological treatment. Certain cells occur scattered about in the tissue which are 
both larger and stain more deeply than their neighbours, but the latter phenomenon 
may be, and probaby is, caused by the presence of tannin. In the parenchyma of both 
the upper and lower side of the pulvinus the connexion appears to be more pro¬ 
nounced in the cells of the middle layer than it is in those either next the epidermis 
or next the vascular bundle; and since the cells are more freely pitted on the longi¬ 
tudinal than on the transverse walls more connexions exist through those of the one 
than of the other. 
With regard to the middle lamella there is some difficulty, unless very careful 
preparation is adopted. It will in any case stain, the depth of the staining depending 
upon the action of the acid and of the dye, and if the treatment with the one or with 
the other be forced, the great coloration of the lamella will so obstruct the view that 
it will be impossible to see with certainty whether or not a distinct continuity of 
the protoplasmic processes occurs. The difficulty may, however, in a great measure 
be removed by long treatment with strong glycerine, which both dissolves the greater 
portion of the colouring matter from the lamella, and at the same time renders it 
sufficiently transparent for a decisive observation to be made. 
The bast fibres of Mimosa are of peculiar interest with regard to this question. 
The middle lamellae between these cells are so little developed that they are re¬ 
cognised with some difficulty, and which is an important fact, do not stain at all. 
Consequently, the additional factor of difficulty, that the presence of a well-developed 
middle lamella involves, is here done away with. Each bast cell is freely pitted, the 
pits of neighbouring cells being placed symmetrically opposite one another, When 
treated with sulphuric acid and stained in the usual manner the following appearance 
is produced. The pit membranes being somewhat thick have distinctly swollen, and 
in so doing have increased the distance from one another of the ends of the proto¬ 
plasmic processes projecting into the pit cavity, All the processes are deeply stained, 
and between each symmetrically opposite pair is a small less stained portion tra¬ 
versing the pit membrane, which from its reactions must be protoplasm. Thus it 
stains with iodine, and when coloured with methyl violet is not dissolved by 
glycerine (Plate 68, fig. 6). It is also well brought out by Hofmann’s blue, the 
staining characters of which have already been sufficiently dwelt upon. That it is 
not callus is clear from the fact that it does not dissolve in sulphuric acid. The 
structure traversing the pit membrane is somewhat difficult to observe, both on 
account of its very small size and its want of definition. Indeed, it rather presents 
the appearance of a small blue cloud between the ends of the deeply-stained and well- 
defined processes. 
The protoplasmic processes projecting into the pits are broad at their extremities, 
and are at the same time more deeply coloured at that point. They gradually taper 
off from the bottom of the pit inwards, widening again as they join the general proto- 
