February i, 1912] 



NATURE 



463 



In East and South Africa are found ^4. mossambica, 

 A. bengalensis, and ^4. bicolor, the range of all of which 

 xtends to the South Pacific. Of these, A. mossambica, 

 mging from the Cape to Zanzibar and the Seychelles, 

 mes nearest to the European species, from which it 

 ifers by the broader bands of teeth. Strange to say, how- 

 '■r, there are no eels in tropical West Africa, this being 

 counted for by " Dr. J. Schmidt, of the Danish Fishery 

 commission, who, with the aid of Danish hydrographers, 

 has ascertained that the water of the great depths of the 

 inter-tropical Atlantic is for the greater part between 4° 

 and 5° C, nowhere reaching the temperature ascertained 

 to be the minimum (7° at a depth of 1000 metres) required 

 for the breeding of the eel in the North Atlantic. There- 

 fore the reason why eels are absent from some of the 

 warmest regions of the world, such as West Africa and 

 tropical South America, is that the deep sea to which they 

 would have to resort for breeding is too cold, an extra- 

 ordinary fact when we bear in mind that, outside the period 

 of reproduction and of larval life, the European eel can 

 accommodate itself to such varied climatic conditions as 

 obtain between the Arctic circle and Nubia. The suitable 

 uiditions for breeding are only to be found in the North 

 lantic, the Mediterranean, and the Indian Ocean ; in 

 consequence eels are only found in those parts of Africa 

 (North, East, South) which are within the migratory 

 powers of the fish." 



In this connection may be quoted a paragraph recently 

 published in the daily Press, that, in order, apparently, to 

 preserve the supply for home waters, " Denmark intends 

 to stop the migration of eels from the Baltic to the outer 

 ocean by pla.-ing a barrier of submerged electric lights 

 between the island of Faroe and the Fyen coast. Eels, 

 which migrate in the dark, will not, it is believed, cross 

 tliis barrier." 



An article on the migration of fishes, including eels, by 

 Mr. V. Franz, appears in the aforesaid issue of Himmel 

 und Erde. 



A summary of reports relative to eel-fry, drawn up by 

 Mr. A. B. E. Hillas, is published in No. ii. of Irish 

 Fisheries Investigations for 1909 (191 1); while No. vi. of 

 the same for 1910 is devoted to an account, by Messrs. 

 Holt and Byrne, of the fishes of the genus Scopelus from 

 the Irish Atlantic slope. 



PAPERS ON PLANT PHYSIOLOGY. 



npHE action of radium compounds on plants is discussed 



■*■ by Prof. H. Moliscii in a short article published in 



the Sitzunf^sberichte dcr ka^serlichcn Akademie der Wisscn- 



schafteti, Vienna (vol. c\x., part v.). Experiments showed 



that sufficient light is emitted by strong preparations to 



produce heliotropic curvature in the case of very susceptible 



plants such as the oat and the common vetch. With regard 



the action of the a, )3, and y rays, it was found that 



igitudinal growth is diminished and that the periods of 



spontaneous nutation are shortened, but they induce no 



form of tropism. 



Prof. J. V. Wiesner contributes to the Sitztnigsberichte 



r kaiserlichcn Akademie der Wisscnschaften, Vienna 



)1. cxx., part iii.), a paper, supplementary to his book, 



cussing further investigations as to the light-regulated 



sition of leaves and the amount of light utilised by plants 



ichtgonuss). In the same publication experiments arc 



cribed by Dr. F. Weber which were intended to throw 



-,lit on the dormant condition of trees and shrubs. Foliow- 



mg up the warm-bath method of forcing proposed by 



Molisch, which showed that individual branches can be 



paratcly resuscitated, the effect of injecting water into 



mches was tried, and also of the mere insertion of the 



ejection syringe. In the case of lilac and the broad-leaved 



iitne, wator injection caused the buds to open three weeks 



J tarlicr than normal buds, while mere pricking produied a 



similar result, though not quite so pronounced. 



With reference to experiments designed to investigate tiie 

 effect of growing plants in air enriched with carbon dioxide, 

 Dr. F. F. Blackman communicates a note to The 

 Gardener's Chrotiiclc (December 2, 191 1) in which he pre- 

 sents an apt illustration of the operations of " limiting 

 factors." When plants are placed in air which contains 

 more than the normal amoiuU of carbon dioxide, if either 



NO, 2205, VOL. 88] 



the light or the temperature is low, the plant may not 

 respond to the increased supply of carbon dio-xide. because 

 assimilation is as great as the amount of light or degree 

 of heat will allow ; the light or temperature may act as a 

 limiting factor. If the light is increased, then plant 

 assimilation may also increase until another limiting factor 

 comes into operation. Therefore in experiments dealing 

 with assimilation, growth-rate, or other physiological pro- 

 cesses it is necessary to consider whether the results ex- 

 pected from improvements of any one condition may not 

 be prevented by the limitation imposed by another factor. 



An account of cotton investigations in Egypt, by Mr. 

 W. L. Balls, published in The Cairo Scientific Journal (vol. 

 v.. No. 60), deals with several interesting problems in gen^'ral 

 plant physiology. The conclusions, based on the study of 

 the root system of the cotton plant, deserve close attention. 

 While examining the effect of temperature upon growth, it 

 was observed that growth of the tap root amounted to half 

 a metre in twenty-four days at a mean temperature of 

 25° C. Considerable importance is attached to checks- 

 imposed upon root growth, whether by interference of other 

 roots or rise of the water-table. It is argued, and experi- 

 ments are cited in proof, that a premature rise of the 

 water-table, as in 1909, must cause untimely shedding of 

 bolls, flowers, and buds. Reference is also made to the 

 previously noted " sunshine eflect," i.e. the complete arrest 

 of main-stem growth during the hottest months whenever 

 the sun shines directly on the plant. 



A contribution to the subject of s.altmarsh and cstuarine 

 vegetation, which deals with the distribution of halophytic 

 plants as controlled by the salinity of the subsoil water, is 

 presented by Dr. J. \V. Harshberger in the Proceedings of 

 the American Philosophical Society, Philadelphia (vol. i.v 

 No. 201). A combined hydrometer and thermometer was 

 used for determining the water density at various stations, 

 where the assemblage of plants was also noted. From the 

 readings taken, maximum and minimum densities were 

 obtained for each plant. Thus Spartina stricia, var. MKirr- 

 tima, which showed the widest range of accommodation, 

 was found growing in water containing as little as 2 and 

 as much as 4 per cent, of salt. For Spartina patens and 

 Salicornia herbacea a similar maximum, but a higher 

 minimum, are recorded. Distichlis spicata, Limonitim 

 caroUniantim, and Jiincus Gcrardi, which follow next in 

 order, have a much narrower range. .\ remarkably low 

 maximum is recorded for Suaeda inarHima. 



In connection with the condition of apples appropriately 

 l<nown as " bitter pit," which has supplied fungologists 

 and others with a puzzling problem, an explanation ascrib- 

 ing the cause to poisonous effects produced by arsenical 

 sprays has been put forward in the Proceedings of the 

 Royal Society of Victoria (vol. xxiv., part i.) by Dr. Jean 

 White ; the arguments are rational, and if substantiate<l 

 will lead to a more careful consideration of spray eflfects. 

 The author had had the opportunity of making a few 

 trials with sprayed and unsprayed trees which bear out the 

 explanation, but the opinion is expressed reservedly and 

 published in order to induce fruit-growers to put the theory 

 to test. 



A PHOTOGRAPHIC STIDV Oh \i>h'TF\ 

 RINGS IN LIQUIDS. 

 "piIOUGIl the laws of vortex motion have 

 ^ extensively examined by the ablest mathematicians, 

 comparatively few experiments appear to have been niado 

 to study the nature of these motions in air and liquids 

 beyond some experiments made about 1867 by Prof. P. <i. 

 Tait, who examined the properties of' .smoke rings in yr. 

 In an extended experimental investigation of this subject 

 the present writer found that very beautiful vortex motions 

 may be easilv produced in such high-density fluids as wator 

 and oils which have free surfaces and small viscosity. 

 The study consisted in examining the various properties of 

 single and double rings, both visually an<l with the aid of 

 the camera. 



.\ tank was constructed which woukl permit the rings 

 to be observed from the two sides, the top, and one end. 

 This tank was made with sides of plate glass. It wa« 

 151 cm. long, 59-5 cm. high, and 12 cm. wide. For the 

 pi-oduttidii i)f til'- lings a cylindrical metal can was pr«>- 



