22 Life and Immortality. 
according to the size of the leaf, are left open for a short 
time before the edges of the lobes come into contact, 
consequent upon the intercrossing of the tips of the mar- 
ginal spikes first, thus enabling an insect whose body is not 
thicker than these measurements to escape, when disturbed 
by the closing lobes and the increasing darkness, quite easily 
between the crossed spikes. Moderately sized insects, if they 
try to escape between the bars, will be pushed back into the 
horrid prison with the slowly closing walls, for the spikes 
continue to close more and more until the lobes are brought 
into contact. Very strong insects, however, manage to effect 
their release. It would manifestly be a great disadvantage 
to the plant to remain many days clasped over a minute 
insect, and as many additional days or weeks in recovering 
its sensibility, inasmuch as a very small insect would afford 
but little nourishment. Far better would it be for the plant 
to wait until a moderately large insect was captured, and to 
allow the little ones to escape, and this advantage is gained 
by the slow intercrossing of the marginal spikes, which, 
acting like the large meshes of a fishing-net, allow the small 
and worthless fry to pass through. 
Touching any one of the six filaments is sufficient to 
cause both lobes to close, these becoming at the instant 
incurved throughout their entire breadth. The stimulus 
must therefore radiate in all directions from any one fila- 
ment, and it must also be transmitted with considerable 
rapidity across the leaf, for in all ordinary cases, as far as the 
eye can judge, both lobes close at the same time. Physiolo- 
gists generally believe that in irritable plants the excitement 
is transmitted along, or in close connection with, the fibro- 
vascular bundles. Those in Dionza seem at first sight to 
favor this belief, for they run up the mid-rib in a great bun- 
dle, sending off small bundles almost at right angles on each 
side, which bifurcate occasionally as they stretch towards 
the margin, the marginal branches from adjoining branches 
uniting and entering the marginal spikes. Thus a continuous 
