122 



NATURE 



[November 29, 1900 



on the one hand, and the integumented megasporangia of cer- 

 tain Palaeozoic Lycopods on the other. The latter organs pre- 

 sent close analogies with true seeds, but are wholly distinct in 

 detailed structure from the Gymnospermous seeds above men- 

 tioned. The discovery of the specimens of the new cone is due 

 to Messrs. J. Lomax and G. Wild, who recognised it as a 

 Cardiocarpon-ht2LXV[\^ strobilus, resembling a Lepidostrobtis. 

 The original specimens, which are calcified and generally well 

 preserved, were derived from the Ganister beds of the Lower 

 Coal-measures of Lancashire. A closely similar fructification 

 occurs, at a much lower horizon, in the Burntisland beds of the 

 Calciferous Sandstone Series. 



The strobilus is of the ordinary Lepidostrobiis type. The 

 cylindrical axis bears numerous spirally disposed sporophylls, 

 each of which consists of a long horizontal pedicel, expanding 

 at the distal end into a rather thick lamina, which turns verti- 

 ca'' V upwards. Anatomically, the structure is also that of a 

 Lej>idoslrobus. The ligule is sometimes well preserved ; it is 

 seated in a depression of the upper surface of the sporophyll, at 

 the distal end of the sporangium, and is thus in the normal po- 

 sition. 



With one exception, the specimens of the strobilus are imma- 

 ture, and their tissues not quite fully differentiated. These 

 younger specimens bear sporangia which are essentially those of 

 a Lepidostrobus. A single large sporangium is seated on the 

 upper surface of the horizontal pedicel of each sporophyll, to the 

 ■median line of which it is attached along almost its whole 

 ilength. The sporangial wall has the structure characteristic of 

 Lepidostrobus. Within the sporangial cavity, the membranes of 

 ■the megaspores are usually preserved ; a single large megaspore 

 ^most fills the sporangium, but smaller, abortive spores, with 

 thicker walls, are also present. It appears that a single tetrad 

 was developed in each megasporangium, and that of the four 

 sister-cells one only came to perfection, constituting the func- 

 tional megaspore. 



In one specimen, discovered by Mr. Wild, the strobilus is in 

 a more advanced condition. In its upper part the sporophylls 

 simply bear sporangia, as above described, but lower down in 

 the cone these are replaced by integumented, seed-like struc- 

 tures, identical with the detached bodies called Cardiocarpon 

 ..anomalum by Williamson. Mr. Wild's specimen, then, demon- 

 strates that the Cardiocarpon anomalum of Williamson was 

 Jjorne on a cone with all the characters of a Lepidostrobus, and 

 that it represents the matured condition of the megasporangium 

 and sporophyll. 



The detailed comparison of specimens in the young and the 

 mature condition has shown the nature of the change, which 

 Converts the megasporangium, together with its sporophyll, into 

 a seed-like organ. A thick integument has grown up from the 

 .<=porophyll, completely overarching the megasporangium, except 

 for a narrow crevice left open at the top. When seen in a 

 section tangential to the strobilus as a whole, this crevice is cut 

 across, and presents exactly the appearance of a micropyle ; in 

 reality it differs from a micropyle in being a narrow slit, ex- 

 pending almost the whole length of the sporangium, in the 

 ftadial direction, whereas the micropyle of an ordinary seed is a 

 imore or less tubular passage. 



In a strobilus associated with the seed-like specimens, and 

 •.probably of the same species, but bearing microsporangia, it 

 was found that the latter, like the megasporangia of the female 

 -cone, are provided with integuments. 



The Burntisland specimens, which from their horizon are 

 presumably of a distinct species, are of interest for two reasons : 

 in one specimen the ligule is clearly shown, enclosed by the 

 integument, the only example of this organ so far observed in 

 the mature, seed-like stage of the fructification. Another of 

 the Burntisland specimens was the first observed in which the 

 prothallus was present. It fills a great part of the functional 

 megaspore, which is almost co-extensive with the sporangial 

 cavity, and consists of a large-celled tissue, resembling the pro- 

 thallus of Isoetes or Selaginella. The peripheral prothallial cells 

 are smaller than the rest, but no archegonia could be detected. 

 [In a section, since examined, cut by Mr. Lomax from one of 

 the Coal-measure specimens, the prothallus is even better pre- 

 served. October 9, 1900.] 



The bodies described in this note resemble true seeds in the 

 possession of a testa or integument, and in the fact that one 

 megaspore or embryo-sac alone came to perfection ; the seed- 

 like organ was likewise shed entire, and appears to have been 

 indehiscent. In many points of detail, however, the repro- 



NO. 1622, VOL. 63] 



ductive bodies in question differ from the seeds of any known 

 (iymnosperms ; they afford no proof of the origin of the latter 

 class from the Lycopods. The newly-discovered tructification 

 nevertheless shows that certain Palaeozoic Lycopods crossed the 

 boundary line which we are accustomed to draw between 

 Sporophyta and Spermophyta. As these fossils appear worthy 

 of generic rank, it is proposed to found the genus Lepidocarpon 

 for their reception. 



Physical Society, November 23.— Prof. Everett, F.R.S., 

 Vice-President, in the chair. — A paper on a self-adjusting 

 Wheatstone's Bridge, by E. H. Griffiths and W, C. D. 

 Whetham, was read by Mr. Whetham. The object of this 

 paper is to describe a cheap and easy method of getting a self- 

 adjusting bridge to show on a scale the actual resistance of any 

 wire. Contact with the bridge wire is made by means of a 

 light horozontal bar, which is suspended by a phosphor-bronze 

 strip from the coil of the d'Arsonval galvonometer used with the 

 instrument. A second bar, parallel to and above the first, is 

 rigidly connected with the coil. A wooden beam, worked by 

 clockwork, moves up and down between the bars and clamps 

 them alternately. When the beam is down contact is made 

 with the bridge wire. If this contact is not at the zero point 

 a current will flow through the coil, and if the cell is connected 

 up the proper way, it will turn the coil so as to bring the upper 

 bar nearer to the null point. This puts a twist into the phosphor- 

 bronze strip, and when the beam rises and clamps the upper 

 bar the torsion comes into play, and brings the lower bar under 

 the upper one. The beam then descends and makes contact at 

 this point, and if any current flows through the galvanometer there 

 is further movement until the null point is reached. Any altera- 

 tion in the resistance of the wire under experiment causes a 

 movement of the zero point on the bridge wire, and this 

 is followed by the lower arm. The position of the lower 

 arm can be directly indicated by means of a scule. 

 Prof. S. P. Thompson asked how the scale was calibrated. Mr. 

 Whetham said the scale was arbitrary, but it could be calibrated 

 by the known resistance of the bridge wire per unit length. 

 Extension of the range can be obtained by shunting the bridge 

 wire with various resistances. Mr. Glazebrook asked how 

 sensitive the bridge was. Mr. Whetham said that working with 

 a dry cell it could easily indicate one degree on a platinum 

 thermometer. Mr. Blakesley pointed out that if the cell was 

 connected up the wrong way the zero point would be an 

 unstable one. — A paper on the liquefaction of hydrogen j 

 was read by Dr. M. W. Travers. These experiments were | 

 undertaken in order to provide liquid hydrogen in sufficient 

 quantity for the separation of neon from the helium with which 

 it is usually mixed. The separation is efi^ected by cooling the 

 gases to the temperature of hydrogen boiling at atmospheric 

 pressure. The principles and conclusions do not diff"cr from those 

 of Dewar, but as the production of liquid hydrogen is neither 

 difficult nor costly, an account of the experiments is given. In 1884 

 Wroblewski showed that strongly cooled and compressed hydro- i 

 gen, on being allowed to expand, formed mist or spray in the tube ; ' 

 and later Olszewski repeated these experiments on a larger scale 

 and determined the temperature of the liquid. Other methods 

 of liquefying hydrogen have been suggested by Lord Rayleigh 

 and Kammerlingh Onnes. In the case of many gases a fall of 

 temperature takes place on free expansion, but under ordinary 

 circumstances the temperature rises in the case of hydrogen and 

 helium. The principle of free expansion was first applied by 

 Hampson and Linde to the liquefaction of air. Within the last 

 two years Dewar has shown that, at a temperature close to 

 -200° C. , hydrogen behaves as an imperfect gas and becomes 

 cooled when allowed to expand. This principle has been ap- 

 plied by Dewar to the liquefaction of hydrogen in quantity. In 

 the author's experiments, hydrogen under a pressure of 200 

 atmospheres passes through a coil which is cooled to - 80° C. 

 by a mixture of solid carbonic acid and alcohol. It then enters 

 another coil contained in a chamber which is continually re- 

 plenished with liquid air. The lower portion of this coil passes 

 into another chamber, which is closed and communicates through 

 a pipe with an exhaust pump. Liquid air flows continuously from 

 the first chamber into the second through a pin valve controlled by 

 a lever. The liquid air, boiling undera pressure of 100 mm. of mer- 

 cury, lowers the temperature to -2cx)°C. The gas then passes into 

 a regenerator coil, which is enclosed in a vacuum vessel, and 

 expanding at a valve, passes upwards, through the interstices of 

 the coil and the annular space surrounding the chambers through 



