514 



NATURE 



\Oct. 14, 1875 



a particular cell-fluid, on the molecular condition of the cell- 

 wall, &c., on temperature, and on the pressure of the air. But 

 these conditions are continually varying, and the equilibrium con- 

 tinually disturbed." That a turgescence such as M. Royer 

 describes occurs in many cases is well known, Space does not 

 allow a detailed description of the physiological mechanism, but 

 nearly all we yet know may be found in Sachs, who, however, 

 attributes the phenomena directly solely to the passage of water 

 and the elasticity of the cell-walls. Indirectly the cause may 

 very possibly be heat acting as M. Royer supposes. It would 

 be interesting to learn the effect of pollination on these plants, 

 especially whether after it had taken place Vidoi-ia regia would 

 re-open. G. S. Boulger. 



S, Westbury Road 



Dehiscence of the Capsules of Collomia 

 In Mr. Duthie's very interesting account (vol. xii. p. 494) of the 

 mode of dehiscence of the ca[)sules of this plant, he suggests that 

 the purpose of the projection of the seeds on to the viscid hairs of 

 the plant itself may possibly be found in its enabling the plant to 

 live on its own seeds. Surely this is a superfluous and needlessly 

 improbable hypothesis. The violent discharge of the seeds is 

 undoubtedly one of the modes adopted by nature for their dis- 

 persion to plots of ground where the mineral constituents of the 

 soil which they mainly require have not been entirely used up by 

 the parent plant. Their interception by the parent plant is no 

 doubt accidental. The purpose served by the viscid hairs of 

 this and other plants .'-till remains to be discovered if we follow 

 the clue afforded by Mr, Darwin's observations on in?; ctivorous 

 plants. The violent expulsion of the seeds from the ripe capsule 

 is a much more common phenomenon than that which we have 

 exhibited in Collomia, together with a few other plants, as 

 Acanthus, Ruellia, Eschscholtzia, and Geranium, where the whole 

 fruit is thrown off together. Mr. Duthie will find a good 

 description of the phenomenon in Hildebrand's "Die Schleu- 

 derfriichte und ihr im anatomischen Bau begriindeten Mechanis- 

 mus," in Pringsheim's "Jahrbui^h" for 1873-74, The author 

 draws an interesting comparison between the structure of 

 Collomia, with its single seed in each division, and its apparatus 

 for projecting these to a distance, and that of the allied genus 

 Cilia, with its numerous seeds in each division, which possess no 

 such mechanism, but which, being much lighter, are conse- 

 quently more easily dispersed by the wind. 



Alfred W. Bennett 



Oceanic Circulation 



Mr. Croll's statement (vol. xii. p. 494), that the North Atlantic 

 in lat. 38° is above the level of the equator, is based partly^on the 

 C/'rt//w^^soundings and partly on Muncke's determinations of the 

 thermal expansion of sea- water, which, however, were not made on 

 sea-water at all, but on a saline solution prepared for him by 

 Leopold Gmelin, according to data furnished by the incomplete 

 analyses of Vogel and Bouillon La Grange. As Mr. Croll's 

 statement depends on such very minute difterences of volume, I 

 am led to ask him to compare the rate of expansion of real sea- 

 water, as determined by Prof. Hubbard, with Muncke's table ; 

 he will notice a discrepancy sufficiently wide to make it a matter 

 of interest to ascertain how far the employment of the American 

 observations may serve to substantiate or modify his conclusion. 



Yorkshire College of Science, Oct. 11 G. E. Thorpe 



High Waves with a North-west Wind 



Your correspondent Capt. Kiddle has again called attention 

 (vol. xi. p. 386) to the greater height of waves raised by a north- 

 west wind, over those raised by a S.W. wind. I have observed 

 the fact twice in the mid- Atlantic, but also very often on the west 

 coast of Scotland, from which it is evident the phenomenon can 

 be due to no particular combination of currents. 



An examination of synoptic charts, for the dates of many 

 cases, has convinced me that the phenomenon is due to the 

 nature of the circulation of the air in a cyclone. 



In the south-east portion of a cyclone, where S.W, winds are 

 found, the wind seems to blow along and almost off the surface 

 of the sea ; while in the south-west portion, where N, W, winds 

 are found, the wind seems to bear down on the sea, and 

 " harrow " it into streaks of foam. 



A perfectly analogous phenomenon appears in dust whirls, 

 where to the right front_of the centre the dust is closely packed, 



and tends to rise off the ground ; while behind the centre the 

 dust is "raked" into streaks by the more downward direction 

 of the blast. 



The portion of the Atlantic about 45° N. latitude, and between 

 40° and 50° W. longitude, where Capt. Kiddle has observed such 

 high waves, has long been known as the "Roaring Forties." 

 An examination of synoptic charts of the North Atlantic, for 

 every day of the year 1865, show.s that the bad weather in those 

 parts is generally due to one of two conditions of the distribution 

 of atmospheric pressure. 



In the commoner case, the great area of high barometric 

 pressure, which constantly covers the North Tropical Atlantic, 

 stretches northwards to the east of Newfoundland like a wedge, 

 on the east side of which cyclones are formed which go in an £. 

 or N.E. direction. 



In the rarer but more violent case, the great Atlantic area of 

 high pressure rises into two heads or humps, one about Madeira, 

 the other about Bermuda, stretching up to Newfoundland. 

 Cyclones coming from Labrador work round this hump to the 

 S.E., and die out in mid- Atlantic. In either case gridients for 

 N.W. winds, often very steep, are formed between the fortieth 

 and fiftieth parallels of longitude, Ralph Abercrombv 



21, Chapel Street, S,W., Oct, i 



Diatoms 



I HAVE reason to think that I have made a discovery which 

 may change the ideas of naturalists as to the nature of some 

 Diatoms. 



In co)X^c\xs\g Di itomacea: I have found a species of N'avicula (?) 

 which is invested with a gelatinous envelope, and from the edges 

 of the frustule project a numbsr of long processes or arms of the 

 same soft nature. These vary much in number, in some speci- 

 mens being eight or ten, and in others as many as twenty-five or 

 even more. They are longer than the frustule, and radiate from 

 it with much regularity. The Diatoms when detected (upon a 

 floating fucHs common in the sea hereabout) were dead, and I 

 was unable to detect any movements. 



a, the frustule : b, the gelatinous envelope projecting beyond the margin ; 

 ^c c, the processes, or pseudopodia. 



T have examined so many individuals of this Diatom that I 

 think it hardly likely that I have been deceived, as they are by 

 no means very minute, 



Dr, Carpenter, in the fifth edition of his admirable work on 

 the microscope, speaks of some observations by Mr. Stevenson 

 on the genus Coscinodiscus, which hint at the possibility of some 

 Diatoms having appendages projected through apertures of the 

 frustule. The highest power of my microscope is one of Messrs. 

 R, and J, Becks, |th, a very fine glass. 



I propose to forward as soon as possible the sticks, dry and in 

 balsam, as well as the "gathenng" in spirits, to a competent 

 diatomist, who will confirm my observations if correct, and I 

 send this to Nature to ;^secure priority in case I have really 

 made a discovery, ' W, W, Wood 



Manila, July 20 



