190 COHN, ON THE CONTRACTILE 
the cells more or less rapidly ; and as this takes place, the 
outline of the cells becomes undulated, whilst at the same 
time their walls are partially separated by a wider interval. 
After a little time the transverse striation of the cells is 
manifest throughout. The most extreme degree of shortening 
of a filament, and at the same time the closest transverse 
striation of its cells, is seen when it is brought in contact 
with a drop of sulphuric acid; by this reagent all the cells 
are rendered of a lemon-yellow colour, whilst the scattered 
pollen-grains, from the coloration of their membrane, become 
purple-violet. Concentrated sulphuric acid soon destroys the 
cell-wall, leaving only the cuticle, which is ultimately black- 
ened. Potass also colours the cells yellow and corrugates 
them very deeply, whilst the membrane of the pollen-grains 
assumes a beautiful brown-red hue. Nitric acid, which gives 
the cells a pale-yellow colour (orange-red after addition of 
potass), contracts the cell-membrane, but it causes a remark- 
able distension of the cuticle, which is thus raised up in the 
form of an elevated pouch from the epidermis, and is de- 
tached even from the hairs. 
Tf the filaments are crushed under strong pressure, the cells 
are unable to contract; but as soon as the covering-glass is 
raised, all the cells in an instant exhibit the transverse stria- 
tion. The ruge, however, owing to the far too rapid contrac- 
tion, are very irregular, and whole masses of cells, under 
these circumstances, may be seen to become curved. 
Although at present Professor Cohn has been unable to 
observe the action of transitory irritation upon the form of 
the cells, since the filaments which have been penetrated by 
water no longer react, he entertains no doubt that the mo- 
mentary contractions caused by irritants depend, equally with 
the permanent shortening consequent upon death, upon the 
transverse corrugation of the cells. 
It would seem, therefore, that the contractile cells of the 
Cynarez correspond in their behaviour essentially with those 
of unstriped muscle, and we may now be said to be acquainted 
wilh plants in reality (so to speak) furnished with muscles. 
The contractile cells are distinguished by the extreme 
delicacy of their wall, which is thinner than in any other 
tissue with which Professor Cohn is acquainted. It is only 
the extremities of the filaments upon which the anther is 
supported that are found to be composed of short, square, very 
thick cells, but these are evidently not contractile. Pro- 
fessor Cohn had on a previous occasion shown that the fila- 
ments become thickened in the same proportion that they 
diminish in length. A filament, for instance, that before 
