188 COHN, ON THE CONTRACTILE 
remarked that after spontaneous or natural death the fila- 
ments contract to the utmost. 
Although, eventually, the pistil may project about 5 mm. 
beyond the anther-tube, this arises in the smallest possible 
degree from the growth of the pistil itself, after the flower 
has burst. The true cause of the apparent elongation is 
the retraction of the anther-tube by the shortening of the 
filaments after their death, and in consequence of which the 
tube will at length be found | to 1 mm. below the summit of 
the corolla, above which, a few hours before, it had pro- 
projected 3—4 mm. 
Having a short time since obtained a new microscope by 
Hartneck, Professor Cohn determined to imvestigate the 
anatomical changes undergone by the contractile filaments in 
their contraction. 
In order to examine the filaments in the elongated irritable 
condition, it is necessary, first of all, to remove the air with 
which certain passages in the internal tissue are partially 
filled, and owing to which the transparency of the tissue is 
much impaired. 
The air may be removed by placing upon a filament sur- 
rounded with water, a covering-glass, upon which the ob- 
jective is screwed down with moderate force, and so as to 
subject the filament to a slight compression. The object is 
then to be pushed for its entire length under the objective. 
By this means the whole of the 
Vie. a. Fie. 2, air is, aS it were, squeezed out, 
and its place supplied with the 
water or glycerine, as the case 
may be; and the internal tissue 
covering the epidermis readily 
brought in view. 
The tissue of the filament con- 
sists of a central vascular bun- 
dle, containing principally an- 
nular and closely wound spiral 
vessels, and surrounded by rows 
of elongated cylindrical cells, 
placed one above another, and 
separated by straight, transverse 
dissepiments. (Fig. a.) 
Externally the filament is co- 
vered with an epidermis com- 
posed of similar cells, which, on 
the upper side, are thicker and 
convex, so that the filament appears, as it were, to be grooved, 
