56-' 



NA TURE 



[Oct. 9, 1884 



It is impossible to put in a short space all the reasons 

 which led Sachs to draw a sharp distinction between the 

 behaviour of water entering into preformed capillary 

 cavities or interstices, and water which is " imbibed," i.e. 

 forces its way between the molecules or micellae of an 

 organised bod}'. It may be remarked that cases may 

 easily be supposed where it would be difficult to draw the 

 line, and it is certainly not easy to see why " imbibed " 

 water should be held less fast than water in capillary 

 interspaces. It is just here, in fact, that the assumption 

 of the extraordinary conductibility of wood comes in. 



It is clear, then, that the great difficulty which is to be 

 put aside by assuming, with Sachs, that the water of 

 transpiration is held in a peculiar mobile condition in the 

 substance of the cell-walls, is that of accounting for the 

 great height of the water columns in tall trees. The old 

 capillary theory will not explain this away, because, 

 although the requisite columns of water could be sup- 

 ported, the water could not be moved as required. 



Frederick Elfving brought forward an awkward objec- 

 tion to Sachs's theory a couple of years ago. By stopping 

 up the lumina of the cells and vessels in such a manner 

 that the edges of the cut elements could still be exposed, 

 it was shown that no water could be pressed through a 

 piece of wood. He showed, moreover, that coloured 

 solutions passed into the cavities of the wood-cells 

 through the thin membranes of the bordered pits, but — 

 as must be concluded from his results — not through the 

 thick substance of the walls. Objections have been 

 raised to some details, but it seems difficult to avoid the 

 conclusion that Elfving's results contradict every other 

 view than that the water passes through the thin mem- 

 branes of the bordered pits, and through the cavities of 

 the elements, and not through the main substance of the 

 walls of the lignified cells. 



Elfving has recently published a paper on this sub- 

 ject (" Acta Soc. Scient. Fen. niece," t. xiv. 1884) pro 

 posing an important modification of the views hitherto 

 held. It is needless to go into the reasons why the theory 

 of gaseous pressures generally must be abandoned, even 

 in its later form, as was Boehm's air-pump theory before ; 

 though it is instructive to note that much insight into the 

 physics of the plant may be obtained by a careful study 

 of Boehm's, and especially Hartig's, views, and the various 

 criticisms of them. We may, however, summarise Elfving's 

 remarks, and the chief points for criticism in all the views, 

 as follows. 



In advocating the " imbibition theory," no proof is 

 afforded that the lumina of the elements of the living 

 wood are ever entirely devoid of water : some water is 

 always present at least in the cells. This does not go 

 against either theory ; but the proof that the cells were at 

 any time entirely devoid of water would decidedly support 

 the " imbibition theory." 



Enough has already been said as to why we may reject 

 the theory of atmospheric pressure. 



Confining our attention to the wood of Conifers, for 

 obvious reasons, the chief facts are as follows. As the 

 young wood-cells lose their protoplasm, water, containing 

 air in solution, occupies the cavity, and bubbles of air are 

 formed alternating with drops of water — in fact, a series 

 of " chapelets de Jamin " are formed ; only, instead of 

 being simple and in one long tube, each one is complex, 

 and the broken water-columns are confined in closed 

 chambers permeable (to water, but not to air) at the 

 bordered pits, and therefore communicating. One ad- 

 vantage of this is that the " chapelets " are less easily 

 broken. 



Elfving then passes on to show that, according to 

 Jamin's researches, these columns of water may be of any 

 height likely to come under our consideration : we have 

 thus no more difficulty as to the suspension of the con- 

 tinuous columns of water — continuous, that is, in a ser- 

 pentine course. The molecules of water can pass between 



the supporting bubbles of air as if they had no weight, 

 since it is only the movement of the masses of water as 

 a whole in the longitudinal direction which is prevented 

 by the capillary forces in the" chapelet de Jamin" '; the 

 individual particles of water have perfect freedom of 

 motion, and will of course travel towards the transpiration 

 surfaces. 



Elfving then goes on to show that many other facts are 

 explained by his theory, and especially the loss of con- 

 ductivity for water in branches cut off in the air. We 

 must refer the reader to the original paper, however, for 

 further details. 



In conclusion, while there is no doubt that Sachs's in- 

 genious " imbibition theory " of the ascent of the water in 

 plants was startling, on account of the bold assumption of 

 the peculiar condition of the water in the cell-walls, it 

 must not be forgotten that it was suggested after a series 

 of profound researches into the properties of wood, and 

 by a master-mind which had tried all previous explana- 

 tions and found them wanting; moreover, the strangeness 

 of an hypothesis is in itself no argument, and so long as 

 the "imbibition theory" explains more facts than any 

 other it must be accepted on those terms. 



If, however, the theory proposed by Elfving turns out 

 to explain the same number of facts equally well, it will 

 have to be allowed that it rests on a foundation of a very 

 different nature, and which can be experimentally tested. 

 It is not easy to suggest a distinctive name for the latter 

 theory ; perhaps it might be known as the " step" theory, 

 since the intra-cellular movement of the water up to the 

 leaves seems to be somewhat of the nature of a series of 

 ascents by steps, or from side to side. We recommend 

 the subject to the careful consideration of those physicists 

 who have an adequate knowledge of the structure of 

 plants. 



NA TURAL SCIENCE IN TASMANIA 

 A LTHOUGH the scientific energy of Tasmania is not 

 -**• all that could be wished for, still the Royal Society 

 of Tasmania is doing something to keep the flame alive. 

 It is much to be wished that some of its hundred 

 Fellows would devote themselves to an investigation of 

 the flora and fauna of their districts, about which there is 

 still much to be learnt. The Proceedings of the Royal 

 Society for 1882 and 1883 have just reached us. The 

 volume for 1882 contains over 180 pages, and is illus- 

 trated by four creditably executed lithographic plates. 

 The details of the proceedings at the monthly meetings 

 of the Society are first given, then follow the papers, the 

 more important of which are as follows : — On the fishes 

 of Tasmania, with a classified catalogue of the hitherto 

 recorded species, by Robert M. Johnston. Incidentally 

 he mentions that out of a population of 120,000 persons, it 

 is estimated that about 1050 persons are directly depen- 

 dent upon the capture and sale of fish. Hobart is the 

 chief centre of the industry. Out of the 188 known 

 species, about one-third are regarded as good edible fish, 

 though only some 21 of these are sufficiently abundant to 

 be ranked as of importance from a food point of view, 

 and of these, some, like the sprat and anchovy, are quite 

 neglected, from want of knowledge and want of energy. 

 Among the so-called fresh-water fish, Lates colonorum, 

 though a well-known fish in Australian waters, is confined, 

 so far as is yet known, in Tasmania to one small river 

 discharging into Anson's Lagoon, on the north-east of the 

 island. Though not a sea-going fish, it is chiefly to be 

 found at the mouth of small streams whose connection 

 with the sea is frequently closed by shifting sand-bars ; 

 and possibly in this way it became originally acclimatised 

 to fresh water. The fresh-water herring [Prototroctes 

 marcena) is said to be the finest of the native fresh-water 

 fishes ; chiefly insect-feeders, theygivetheanglersome sport. 

 Some fourteen years ago they suddenly almost disappeared 



