PROTOPLASM THROUGH THE WALLS OF VEGETABLE CELLS. 
837 
means of saturated, watery, picric acid. Absolute alcohol is quite unsatisfactory. In 
the same way sulphuric acid causes very great contraction, the processes being usually 
ruptured, and nearly always pulled perceptibly from the pit membrane. 
The cell-walls possess that peculiar semi-horny structure which is equally shared by 
so many of the Leguminosse, and swell greatly with sulphuric acid. The delusive and 
at the same time very beautiful effects obtained by staining a section after treatment 
with sulphuric acid with methyl violet have already been dealt with under the head 
of pit membrane (Plate 68, fig. 10). As there mentioned, the bottom and sides of the 
pits are markedly stained by this reagent in a way somewhat similar to that of the 
protoplasm, and at first sight the appearance suggests that the cells are freely connected 
—the one with the other—by unbroken protoplasmic threads. The whole structure is 
remarkably like that of an enlarged representation of free cell formation. However, on 
treating the section with glycerine, all the deception disappears with the solution of 
the colouring matter, and it will then become apparent that in reality the connexion 
is neither so well defined nor so pronounced as in the case of Mimosa and Robinia 
(Plate 68, fig. 11). In no instance, so far as I can ascertain, do the processes approxi¬ 
mate to one another in the unbroken way in which they appear to do in Mimosa. In the 
larger cells occupying the middle layer between the epidermis and vascular bundle, the 
protoplasm is either entirely pulled from the pit membrane, or the processes which at 
first connected the protoplasm of the pit with the general protoplasmic mass are 
ruptured so as to leave a short portion only sticking to the pit membrane. In the 
four last layers of cells which abut on to the vascular bundle where the cells are 
smaller with thicker walls and smaller vacuoles, it will be seen that although shrinking 
has taken place, yet the whole appearance of contraction is not so great although 
the protoplasm projecting into the pits has, as a rule, been pulled from the pit mem¬ 
brane. In the swollen pit membrane between the two symmetrically placed processes 
the same stained structure is apparent as occurs in the bast fibres of Mimosa, although 
the whole appearance is much more marked (Plate 68, fig. 11). The stained portion as 
before, and more markedly, suggests an appearance of striation, but with the strongest 
powers at my disposal, consistent with clear definition, I was unable to resolve the 
structure into fine threads. All that one can say is that its reactions point to its 
protoplasmic nature. In such of the other cells of the larger celled tissue as could be 
favourably observed, the same structure was present. It may here be mentioned that 
in cases, e.g., Phcenix (Plate 69, fig. 13), where with a high power a sieve plate 
arrangement can be seen, and the threads clearly made out ; with a low power the 
same appearances are produced as in the case in point, or as in bast fibres, and it seems 
probable that here a sieve plate arrangement does in reality occur. 
The staining of that portion of the pit membrane which colours with aniline blue or 
which is left stained by methyl violet after prolonged action of glycerine, must not be 
confounded with the coloration of the bottom and sides of the pit which occurs with 
methyl violet alone or with methylene blue after the action of sulphuric acid. In 
MDCCCLXXXIII. 5 P 
