Cuar. XIIL] TRANSMISSION OF MOTOR IMPULSE. 253 
ment.—It is sufficient to touch any one of the six filaments to 
cause both lobes to close, these becoming at the same time 
incurved throughout their whole breadth. The stimulus 
must therefore radiate in all directions from any one filament. 
It must also be transmitted with much rapidity across the 
leaf, for in all ordinary cases both lobes close simultaneously, 
as far us the eye can judge. Most physiologists believe that 
in irritable plants the excitement is transmitted along, or in 
close connection with, the fibro-vascular bundles. In Dionzxa, 
the course of these vessels (composed of spiral and ordinary 
vascular tissue) seems at first sight to favour this belief; for 
they run up the midrib in a great bundle, sending off small 
bundles almost at right angles on eachside. These bifurcate 
occasionally as they extend towards the margin, and close to 
the margin small branches from adjoining vessels unite and 
enter the marginal spikes. At some of these points of union 
the vessels form curious loops, like those described under 
Drosera. A continuous zigzag line of vessels thus runs 
round the whole circumference of the leaf, and in the midrib 
all the vessels are in close contact; so that all parts of the 
leaf seem to be brought into some degree of communication. 
Nevertheless, the presence of vessels is not necessary for the 
transmission of the motor impulse, for it is transmitted from 
the tips of the sensitive filaments (these being about the 5\, 
of an inch in length), into which no vessels enter; and these 
could not have been overlooked, as I made thin vertical 
sections of the leaf at the bases of the filaments. 
On several occasions, slits about the 4‘; ofan inch in length 
were made with a lancet, close to the bases of the filaments, 
parallel to the midrib, and, therefore, directly across the 
course of the vessels. These were made sometimes on the 
inner and sometimes on the outer side of the filaments; and 
after several days, when the leaves had reopened, these 
filaments were touched roughly (for they were always ren- 
dered in some degree torpid by the operation), and the lobes 
then closed in the ordinary,manner, though slowly, and some- 
times not until after a considerable interval of time. These 
cases show that the motor impulse is not transmitted along 
the vessels, and they further show that there is no necessity 
for a direct line of communication from the filament which 
is touched towards the midrib and opposite lobe, or towards 
the outer parts of the same lobe. 
Two slits near each other, both parallel to the midrib, 
