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 filament, 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. Physiologists generally believe that in irritable plants the excitement is transmitted along, or in close connection with, the fibro-vascular bundles. Those in Dionæa seem at first sight to favor this belief, for they run up the mid-rib in a great bundle, 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 zigzag line of vessels runs round the whole circumference of the leaf, while in the mid-rib all the vessels are in close contiguity, so that all parts of the leaf seem to be brought into some degree of communication. The presence of vessels, however, is not necessary for the transmission of the motor impulse, for it is transmitted from the apices of the sensitive filaments, which are hardly one-tenth of an inch in length, into which no vessels are seen to enter. Slits made close to the bases of the filaments, parallel to the mid-rib, and thus directly across the course of the vessels, sometimes on the inner and sometimes on the outer sides of the filaments, do not interfere with the transmission of the motor impulse along the vessels, and conclusively show that there is no necessity for a direct line of communication from the filament, which is touched towards the mid-rib and opposite lobe, or towards the outer parts of the same lobe. With respect to the movement of the leaves, the wonderful discovery made by Dr. Burdon Sanderson, and published in 1874, offers an easy explanation. There is, says this distinguished authority, a normal electrical current in the blade and footstalk, which, when the leaves are irritated, is disturbed in the same manner as is the muscle of an animal when contraction takes place.