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Show 248 DROSERA ROTUNDIFOLIA. CHAP. X. divides into two. By loo1ring to either side of the leaf, it will be seen that a branch froin the great central bifurcation inosculates with a branch from the lateral bundle, and that there is a smaller inoscu .. lation between the two chief branches of the lateral bundle. The course of the vessels is very complex at the larger inosculation; and here vessels, retaining the same diameter, are often formed by the union of the bluntly pointed ends of two vessels, but whether these points open into each other by their attached surfaces, I do not know. By means of the two inosculations all the vessels on the saine side of the leaf are brought into some sort of connection. Near the circumference of the larger leaves the bifurcating branches also come into close union, and then separate again, forming a continuous zigzag line of vessels round the whole circumference. But the union of the vessels in this zigzag line seems to be much less intimate than at the main inosculation. It should be added that the course of the vessels differs somewhat in different leaves, and even on opposite sides of the same leaf, but the main inosculation is always present. Now in my first experiments with bits of meat placed on one side of the disc, it so happened that not a single tentacle was inflected on the opposite side ; and when I saw that the vessels on the same side were all connected together by the two inosculations, whilst not a vessel passed over to the opposite side, it seemed probable that the motor impulse was conducted exclusively along them. In order to test this view, I divided transversely with the point of a lancet the central trunks of four leaves, just beneath the main bifurcation; and two days afterwards placed rather larg~ bits of raw meat CHAP. X. CONDUCTING TISSUES. 249 (a most powerful stimulant) near the centre of the disc above the incision-that is, a little towards the apex-with the following results :- (1) This leaf proved rather torpid: after 4 hrs. 40 m. (in all cases reckoning from the time when the meat was given) the tentacles at the distal end were a little inflected, but nowhere else; they remained so for three days, and. re-expandcrl on the fourth Jay. The leaf was then dissected, and the trunk, as well as the two sublateral branches, were found divided. (2) After 4 hrs. 30m. many of tho tentacles at the distal end were well inflected. Next day the blade and all the tentacles at this end were strongly inflected, and were separated by a distinct transverse line from the basal half of the leaf, which was not in the least affected. On the third day, however, some of the short tentacles on the disc near the base were very slightly inflected. The incision was found on dissection to extend across the leaf as in the last case. (3) After 4 hrs. 30 m. strong inflection of the tentacles at the distal end, which during the next two clays never extended in the least to the basal end. The incision as before. ( 4) This leaf was not observed untill5 hrs. had elapsed, and then all the tentacles, except the extreme marginal ones, were found equally well inflected all round the leaf. On careful examination the spiral vessels of the central trunk were certainly divided; but the incision on one side had not passed through the fibrous tissue surrounding these vessels, though it had passed through the tissue on the other side.* The appearance presented by the leaves (2) and (3) was very curious, and might be aptly compared with that of a man with his backbone broken and lower extremities paralysed. Excepting that the line between the two halves was here transverse inste~d of longitudinal, these leaves were in the sam~ state as some of those in the former experiments, with bits of meat placed on one side of the disc. The case of leaf ( 4) * M. Ziegler made similar experiments by cutting the spiral vessels of Drose1·a intermedia (' Comptes renclus,' 1874, p. 1417), but anivecl at conclusions widely different from mine. |
