Mr F. Cohn on the Contractile Filaments in Thistles. 191 
tube. At the time of flowering, this tube is shut in at the 
top, and encloses the style. About this period the anther- 
tube rises to about 4 millimeters above the extreme points 
of the corolla; and if the same is touched, pollen in lumps 
issues from its summit, the anther-tube at the same time 
undergoing a remarkable twisting. After an interval—say 
five minutes—the experiment may be repeated: pollen issues 
anew from the anther-tube, and twisting movements are 
executed as before. The style gradually becomes elevated 
above the summit of the anther-tube, and by the time 
it projects about 4-5 millimeters beyond, the irritability 
has completely disappeared. At this time the style be- 
comes fitted for fertilisation, since the two branches of 
the stigma now first diverge from one another. In general, 
a period of at most twenty-four hours, often less, elapses 
between the commencement and cessation of the irrita- 
bility. When the styles are visible, it is too late for insti- 
tuting experiments. 
These phenomena are produced solely by the contraction 
of the filaments of the stamens, which, on each touch, 
instantly contract, and after a little resume their former 
length. The expulsion of pollen depends upon the an- 
ther-tube being drawn downwards upon the style by the 
contracting filaments, and then pushed up again. The 
contractility of the filaments is most interestingly shown, if 
the stamens are cut away from the corolla. In such a pre- 
paration there is the anther-tube with the five filaments 
depending therefrom; and these latter, on every touch, 
exhibit the liveliest irritability,—throw themselves back- 
wards, straighten themselves again, bend to the opposite 
side, and wind round one another. One might fancy that 
it was a Hydra, rather than a vegetable organism. These 
motions had been previously described by Cohn himself in 
1861, and subsequently by Kabsch (1861), and Unger (1862). 
This contraction may be induced by electrical stimulus. 
Weak currents produce immediate contraction of the fila-. 
ments, which, however, extend themselves after an inter- 
val. Strong currents, on the other hand, kill them at 
once; and in consequence of this, the contracted filaments 
never extend themselves again, but become further short- 
