March r, 1877] 



NATURE 



379 



coral, and the position of the bank in lat. 36° 29' N., long. 

 1 1° 33' W. In other words, Commander Gorringe, on 

 his journey westward from the Strait, after passing over 

 the northern extremity of the deep channel, sounded up 

 the steep slope of the submarine plateau which connects 

 Portugal with Madeira, and within a short distance of a 

 sounding of 1,525 fathoms obtained by H.M.S. Challeti^er 

 on January 30, 1873, in lat. 36° 23' N., long. 11° 18' W. 



The sketch-map does not pretend to be more than an 

 approximation founded upon the still limited number of 

 soundings obtained up to this date, but the bottom-tem- 

 peratures observed in this part of the North Atlantic tend 

 to corroborate the views which I have ventured to ex- 

 press. They show that the submarine flow of cold water 

 of antarctic origin, which has been traced as far north as 

 tiie Bay of Biscay, also fills up the lower depths of the 

 channel which stretches up towards Cape St, Vincent. 

 On the other hand, the channel between the coast of 

 Portugal and the Gettysburg Bank is occupied by the 

 warm water of the Gulf Stream return-current, which, 

 spreading itself out over the banks to westward, explains 

 the presence of the live coral found by Commander Gor- 

 ringe. John James Wild 



HUM MOCK Y MORAINE DRIFT 



DURING his survey of the West Pacific slopes, 

 Clarence King found and has since described, 

 hummocks of moraine drift on the " dying-out glaciers," 

 which are somewhat similar to the "hog-wallows ;" and 

 J. le Conte has described dying- out glaciers and moraine 

 drifts of California. Abstracts of these descriptions will 

 be found in the America?! JoJirnal of Science and 

 Arts, and the full description of the West Pacific 



Perched Erratic Blocks on Croagh-na-Cloosh. 



slopes in Clarence King's report. In West Galway, Ire- 

 land, there are in places large tracts of drift sometimes 

 like Clarence King's description, in others like the " hog- 

 wallow ; " that in the Memoirs of the Irish branch of 

 the Geological Survey have been described as " rocky 

 moraine drift." The accompanying sketch is of some 

 of these drift hummocks on the north slope of Croagh-na- 

 Cloosh, south of Oughterard. G. H. Kinahan 



CONTRACTION OF THE LEAF OF '' DION^A 



MUSCIPULA " i 

 T N the first section of this paper the authors give an account of 

 the mechanical effects which ensue on exciting the sensitive 

 hairs of the Dionaea leaf. The following is a resunit of the 

 principal conclusions at which the authors have arrived : — 



' Abstract of paper on the .Mechanical Effects and on the Electrical Dis- 

 turbance consequent on Excitation of the leaf of Diomea muscipjila, by J. 



If the sensitive hair of a vigorous leaf be touched with very 

 great care by a camel-hair pencil, no visible effect on the leaf 

 will be produced, and a similar gentle contact can be repeated 

 several times before the leaf begins to answer to the excitation 

 by any movement. Sooner or later, however, the marginal 

 liairs bend inwards and the lobe" slightly approach each other. 

 The first efif-ctual exci'ation is followed by an almost imper- 

 ceptible movement ; after this each successive approach of the 

 lobes in nearly every case exceeds that of its predtrcessor. The 

 interval which elapses between excitation and effect diminishes 

 as the extent of the effect increases, both facts having the same 

 meaning, namely that in the plan*^, as in certain cases well 

 known to the animal physiologist, inadequate excitations, when 

 repeated, exercise their influence by what has been termed "sum- 

 mation," and thus the last contraction, that by which the leaf 

 closes, is the result of the summati )n of the excitation which im- 

 mediately preceded it with all the previous excitations. After 

 the leaf has closed it still contracts at each excitation, and 

 attempts to clench itself with greater and greater force. The 

 interval between an excitation and the resulting movement varies 

 from two to ten seconds. 



The authors next proceed to a consideration of the electrical 

 condition of tlie leaf in an unexcited state, which his recently 

 been made the subject of a minute investigation ^ Vjy I'ro*". Munk, 

 of Berlin, who has found — i. That if we conceive the external 

 surface of the leaf divided into strips by parallel lines crossing the 

 midrib nearly at right angles, and coinciding with the veining, any 

 point of the external surface of each strip is negative to any point 

 nearer the midrib. 2. That in comparing different points of the 

 midrib with each other, there is one whose position is two-thirds 

 of the distance from the near to the far end of the midrib, which 

 is positive to the rest. 3. He has further stated that the potential 

 of any point on the internal sarface of the lobe is exactly equal 

 to that of the corresponding and opposite point on the external 

 surface. Of these three proportions the first two are confirmed, 

 in the main, by the authors of the present paper ; as regards 

 normal leaves, however, they take exception to h's conclusions 

 on the two under-mentioned points — {a) That although there is 

 a spot of greatest positivity on the midrib, more or less corre- 

 sponding in position to that mentioned by Pi-of. Munk, yet its 

 position is by no means so definite as Prof. Munk states, but 

 varies in different leaves, {b) That the different points in his 

 isoelectrical negative line are never found to be absolutely iden- 

 tical. From the third proposition the authors generally express 

 their dissent. I'hey, however, content themselves for the present 

 with stating two general conclusions — i. That the part of the 

 midrib which lies nearest the two central sensitive hairs is posi- 

 tive to every other part of the external surface of the leaf, but 

 has usually the same potential as the petiole and other inactive 

 parts of the plant. 2. That the external surface, so long as the 

 leaf is in vigour, is always positive to the internal surface. 



The mettiod used in this research dilfers from that generally 

 employed in previous investigations, relating to animal or plant 

 electricity, in two important particulars : — i. In the adoption of 

 Lippmann's electrometer^ (which has already been used by Prof. 

 Marey in investigations on animal electricity) as the instrument 

 for observing the electrical changes. 2. In the substitution of a 

 constant for a variable potential as a standard of comparison with 

 the potential under investifration. 



In comparing the potentials of two points the following arrange- 

 ment was usually adopted : — The pot containing the plant ^ had 

 been previously kept plunged in water. Three non-polarisable 

 electrodes were used, by one of them (the " fixed electrode ") the 

 damp surface of the pot is connected with the gas-pipes of the 

 building, the other two (•' movable electrodes") are in contact 

 with the two points under observation. By means of a switch, 

 either of these two movable electrodes can be brought into con- 

 nection with one end of the electrometer, the other end being 

 connected with earth. 



When the whole of the outer surface of a leaf is covered with 

 a mass of kaolin, moistened with salt-solution, and brought into 

 connection with one end of the electrometer, the other end being 

 connected by means of the fixed electrode with the petiole or 

 pot, the effect of exciting a sensitive hair is to produce an 



Burdon-Sanderson, M.D., F.R.S , Profesfor of Physiology in University 

 College, and F. J. M. Page, B.Sc , F.C.S. Read before the Royal Society, 

 December 14, 1876. 



' Reichert's and du Bois-Reymond's Archiv, 1876. 



* See the original paper, or Lippman, Pogg. Ann.. 1873, 149, 546. 



3 Most of the observations were made at Kew in the month of August, 

 1876, the plants being obtained from the Royal Gardens, through the kind- 

 ness of the Director. 



