I40 



NATURE 



[December 7, 1893 



west ; Bushire, on the eastern shore of the Persian Gulf, and at 

 Teheran. At Bushire the annual mean for 1878-90 is I2'96 

 inches. Recent observations at Teheran give a mean of about 

 10 inches, and the older observations, taken at the Russian Em- 

 bassy, give a mean of about li inches, of which nearly the 

 whole falls in the winter half of the year. To the north of the 

 great mountain range, between Teheran and the Caspian, 

 the fall is nearly four times as great as in Persia. The same 

 number of the magazine contains a summary of the few meteoro- 

 iojical papers read at the British Association at Nottingham. 



SOCIETIES AND ACADEMIES. 



London. 



Royal Society, November 16. — "Experiments in Heliotro- 

 pism. " By G. J. Romanes, F. R. S. 



I cannot find in the literature of heliotropism that any experi- 

 ments have hitherto been made on the effects of interrupted 

 illumination, when the periods of illumination are rendered as 

 brief as possible — i.e., instantaneous flashes of light. Accordingly 

 I have conducted an extensive research on heliotropism, where the 

 flashes have been caused either by means of electric sparks in a 

 dark room, or by the opening of a photographic shutter placed 

 before the plants in a camera obscura with an arc light or Swan 

 burner, at a distance of several feet on the other side of the shutter. 

 The electric sparks were made either with a Wimshurst machine, 

 induction sparks, or by means of the loUowing contrivance. 

 Fr .m the binding screws of the condenser of a large induction 

 coil copper \a ires were led to a cup of mercury, where, by means 

 of an electro-magnet suitably actuated by clockwork, a current was 

 closed and opened at any desired intervals : each break was there- 

 fore accompanied by a brilliant spark. A thick plate of glass was 

 interposed between the seedlings and the electrical apparatus. In 

 all the experiments here described the plants employed were mus- 

 tard seedlings {Sinapis nigra), previously grown in the dark until 

 they had reached a height of between one and two inches. Save 

 when the contrary is stated, in all the experiments comparative 

 estimates were formed by using the same pot of seedlings : during 

 the first half of a comparative experiment half of the seedlings 

 were protected from the light by a cap of cardboard covering 

 half the pot ; during the second half of the experiment this 

 cap was removed, and the pot turned round so as to expose the 

 previously protected seedlings to the influence of the light. The 

 principal results thus obtamed, and frequently corroborated, 

 were as follows : — 



I. Even having regard to the fact that for equal strengths of 

 a stimulus excitable tissues are more responsive in proportion to 

 the suddenness of the stimulus (or in a kind of inverse proportion 

 to the duration of the stimulus), the heliotropic effects of such 

 flashing stimulation as is above described proved to be much 

 greater than might have been antecedently expected. This was 

 shown to be the case whether the effects were estimated by the 

 rapidity with which the seedlings began to bend after the flashing 

 stimulation was begun, or by that with which they continued to 

 bend until attaining a horizontal line of giowth, i.e. bending to 

 a right angle. 'I'hus, at a temperature ol 70° Fahr., and in a 

 moist camera, vigorously growing seedlings begin to bend 

 towards the electric sparks ten minutes after ihe latter begin to 

 pass, and will bend through 45° in as many minutes ; frequently 

 they bend through another 45" in as many minutes more. This is 

 a more rapid rate of bending than can be produced in the same 

 pot of seedlings when the previously protected side is uncovered 

 and exposed lor similar durations of time, either to constant 

 sunlight or to constant diffused daylight. This is the case even 

 if the sparks (or flashes) succeed one another at intervals of only 

 two seconds. 



II. It would thus appear that the heliotropic influence of 

 electric sparks (or flashes) is greater than can be produced by 

 any other source of illumination. But in order to test this 

 point more conclusively, 1 tried the experiment of exposing one 

 half-pot of seedlings in one camera to the constant light of a 

 Swan burner, and another half-pot of similar seedlings in 

 another camera, placed at the same distance from the same 

 source of light, but provided with a flash shutter working at 

 the rate of two seconds intervals. The amount of bending in 

 similar times having been noted, the pots were then exchanged 

 raid their previously protected halves exposed to the constant 

 and the flashing light respectively. In both cases, the rapidity 



NO. 1 258. VOL. 49] 



with which the bending commenced and the extent to which it 

 proceeded in a given time after commencement, were consider- 

 ably greater in the seedlings exposed to the flashing than to the 

 constant source stimulation. I'he same is true if, instead of a 

 Swan burner, the source of light is the sun. 



III. Many experiments were tried in order to ascertain the 

 smallest number of sparks in a given time which would produce 

 any perceptible bending. Of course the results of such experi- 

 ments varied to some extent with the condition of the seedlings. 

 But in most cases, with vigorous young mustard seedlings and 

 careful observation, bending could be proved to occur within 

 fifteen to thirty minutes, if bright sparks were supplied at the 

 rate of only one per minute. The most extreme sensitiveness 

 that I have observed in these experiments was that of percep- 

 tible bending after half-an-hour's exposure to electrical sparks 

 following one another at the rate of fifty in an hour. This 

 result would appear to indicate that in heliotropism under flash- 

 ing light there need be no summation or "staircase effect"; 

 but that each flash or spark may produce its own effect inde- 

 pendently of its predecessors or successors. 



IV. It is noteworthy that, while the heliotropic effects of 

 flashing light are thus so remarkable, they are unattended with 

 the formation of any particle of chlorophyll. In the many 

 hundred pots, and iheiefore many thousands of plants, which 

 have passed under my observation in this research I have never 

 seen the slightest shade of green tingeing the etiolated seedlings 

 which had bent towards flashing light. On one occasion I kept 

 a stream of 100 sparks per second illuminating some mustard 

 seedlings continuously for forty-eight hours ; and although this 

 experiment was made for the express purpose of ascertaining 

 whether any chlorophyll would be formed under the most suit- 

 able conditions by means of flashing light, no change of colour 

 in any of the .'eedlings was produced. 



With the exception of tho.'c mentioned in the last paragraph, 

 all these results were obtained by using sparks from the coil 

 condenser, as above explained. These sparks were very 

 brilliant, and yielded the maximal results, which alone are here 

 recorded. 



" Experiments in Germination." By G. J. Romanes, F.R.S. 



The primary object of these experiments was to ascertain 

 whether the power of germination continues in dry seeds after 

 the greatest possible precautions have been taken to prevent 

 any ordinary processes of respiration for practically any length 

 ol time. 



The method adopted was to seal various kinds of seeds in 

 vacuum tubes of high exhaustion, and after they had been ex- 

 posed to the vacuum for a period of .ifteen months to remove 

 ihem from the tubes and sow them in flower-pots buried in 

 moist soil. In other cases, after the seeds had been in vacuo 

 for a period of three months, they were transferred to sundry 

 other tubes respectively charged with atmospheres of sundry 

 pure gases or vapours (at the pressure of the air at time of seal- 

 ing) ; after a further period of twelve months these sundry 

 tubes were broken, and their contents sown as in previous case. 

 In all cases, excepting that of clover, the seeds sown were 

 weighed individually in chemical balances, and seeds of similar 

 weights taken from the same original packets were similarly 

 sown as controls. 



The exhaustion of the tubes was kindly undertaken by Mr. 

 Crookes, F. R. S., to whom I must express my best thanks for 

 the assistance he has given. The kinds of seeds used were 

 mustard, red beet, clover, peas, beans, spinach, cress, barley, 

 and radish. In addition to vacuum tubes and control tubes con- 

 taining air, others were charged with oxygen, hydrogen, nitro- 

 gen, carbon monoxide, sulphuretted hydrogen, aqueous vapour, 

 ether, and chloroform. 



With the exception of the beans, where only two were sown, 

 ten weighed seeds were sown out of each of the tubes, 

 and also out of each of the control packets which had 

 been kept in ordinary air from the first. These results 

 amply prove that neither a vacuum of one-millionth of an 

 atmosphere, nor the atmospheres of any of the gases and vapours 

 named, exercised much, if any, effect on the germinating power 

 of any of these seeds. I may add that the same remark applies 

 to an atmosphere of carbon dioxide, although in the particular 

 series of experiments quoted this gas was accidentally omitted. 



A subsidiary object ol these experiments was to ascertain 

 whether any appreciable variations would be caused in plants 

 giown from seeds which, before germination, had been sub- 

 mitted to the conditions above explained. Hundreds of plants 



