568 



NATURE 



[Oct. 13, 1 88 1 



duced beyond certain limits. As regai'ds the chemical products 

 it was thou;^ht that tlie!e would prove rather beneficial than 

 otherwise, in furnishing the very ingredients upon which plant- 

 life depends, and further that the constant supply of pure 

 carbonic acid resulting from the gradud combustion of the 

 carbon electrodes might render a dinjinntion in the supply of 

 fresh air po-sible, and thus lead to economy of fuel. The plants 

 did not, however, take kindly to these innovations in their mode 

 of life, and it was found necessary to put a lantern of clear glass 

 round the light, fur the double purpose of di-charging the 

 chemical products of the arc, and of interposing an effectual 

 screen between the arc and the plants under its influence. 



The effect of interpoi-ing a mere thin sheet of clear glass 

 between the plauts and the souice of electric light was most 

 striking. On placing such a sheet of clear glass so as to intercept 

 the rays of the electric light from a portion only of a plant, for 

 instance a tomato plant, it was observed that in the course of a 

 single night the line of demarcation was most distinctly shown 

 upon the leaves. The portion of the plant under the direct in- 

 fluence of the naked electric light, though at a distance from it 

 of nine to ten feet, was distinctly shrivelled, wh:reas that portion 

 under cover of the clear glass continued to show a healthy 

 appearance, and this line of demarcation was distinctly vi^iLle 

 on individual leaves. Not only the leaves, but the young stems 

 of the plants soon showed signs of de tiuction when exposed to 

 the naked electric light, and these destructive influences were j-er- 

 ceptilile, though in a less marked degree, at a distance of t a enty feet 

 from the source of light. A ques'ion here presents itself that can 

 hardly fail to e-Ncite the interest of the physiological bolanist. The 

 clear gliss does not apparently intercej.t any of the luminous 

 rays, which cannot therefore be the cause of the de-tructive 

 action. Prof. Stokes shoi\ed, however, in 1853, that the 

 electric arc is particularly rich in hijhly refrangible invisible 

 rays, and that the^e are largely absorbed in their passage through 

 clear glass ; it therefore appears reasonable to suppose that it 

 is those highly refrangible rays beyond the visible spectrum that 

 work destruciion on ve,'etable cells, thus contrasting with the 

 lumin )Us rays of less refrangibility, which, on the contrary, 

 stimulate their organic action. 



Being desirous to follow up this inquiry a little further, I 

 sowed a portion of the ground in the experimental conservatory 

 with mustard and other quick-gi-owing seeds, and divided the 

 field into equal rariial portions by means of a framework, ex- 

 cluding diffused light, but admitting light at equal distances 

 from the electric arc. The first section w as under the action of 

 the naked light, the second was covered w ith a pane of clear glass, 

 the third with yellow glass, the fourth with red, and the fifth 

 with blue glass. The relative progress of the plants was nnted 

 from day to day, and the differences of effect upon the deve- 

 lopment of the plants was sufficiently striking to justify the 

 following conclusions : — Under the clear glass the Urgest 

 amount of and most vigorous growth was induced ; the yellow 

 glass came next in order, but the plants, though nearly equal in 

 size, were greatly inferior in colour and thickness of stem to 

 those under the clear glass; the red glass gives lise to lanky 

 growth and yellowish leaf, ^vhile the blue glass produces still 

 more lanky growth and sickly leaf. The uncovered compart- 

 ment shiwed a stunted gro>»th with a very dark and partly 

 shrivelled leaf It should be observed that the electric light was 

 kept on from five p.m. till six a.m. every night except Sundays 

 during the experiment, which took place in January, 1881, but 

 that diffused daylight was not excluded during the intervals ; 

 also that circulation of air through the dividing framework was 

 provided for. 



These results are confirmatory of those obtained by Dr. J. W. 

 Draper ' in his valuable researches on plant cultivation in the solar 

 spectrum in 1843, which led him to the conclu ion, in opposition 

 to the then prevailing opinion, that the yellow ray, and not the 

 violet ray, was most efficacious in promoting the decomposition 

 of carbonic acid in the vegetable cell. 



Having, in consequence of these preliminary inquiries, deter- 

 mined to surround the electric arc with a clear glass lantern, 

 more satisfactory results were soon observable. Thu', peas 

 which had been sown at the end of October produced a haivest 

 of lipe fruit on February 16, under ihe influence, with the excep- 

 tion of Sunday night-, of continuous light. Raspberry stalks 

 put into the house on December 16 produced ripe fruit on 

 March i, and strawberry plants put in about the same time pro- 



' Ste '■ Scientific Memoirs" Ly J. W. Draper, M.D., LL D- Memoir X. 



duced ripe fruit of excellent flavour and colour on February 14. 

 Vines which broke on December 26 produced ripe grapes of 

 stronger flavour than usual on March 10. Wheat, barley, and 

 oats shot up with extraordinary rapidity under the influence of 

 continuous light, but did not arrive at ma'urity ; their growth, 

 having been t .0 rapid for their strength, caused them to fall to 

 the gi-uund, after having attained the height of about twelve 

 inches. 



Seeds of wheat, barley, and oats, planted in the open air and 

 gro« n under the influence of the external electric light, produced, 

 however, more satisfactory results ; having been sown in rows on 

 January 6, they germinated with difficulty, on account of frost 

 and snow on the ground, but developed rapidly when milder 

 weather set in, and showed ripe grain by the end of June, 

 having been aided in their growth by the electric light until the 

 beginuin of May. 



Doubts have been expressed by some botanists whether plants 

 grown and brought to maturity under the influence of continuous 

 light vvuuld produce fruit capable of reproduction, and in order 

 to test this question the peas gathered on February 16 from the 

 plants wdiich had been grown under almost continuous light 

 action weie replanted on February 18. They vegetated in a 

 few days, show ing every appearance of healthy growth. 



Further evidence on the saijie question wdll be obtained by Dr. 

 Gilbert, F.R.S., who has undertaken to experiment upon the 

 wheat, barley, and oats grown as above stated ; but still more 

 evidence will probably be required before all doubt on the subject 

 can be allayed. 



I am aware that the great weight of the opinion of Dr. Darwin 

 goes in favjur of the view that many plants, if not all of them, 

 require diurnal rest for their normal development. In his great 

 work on " The Movements of Plants" he deals in reality with 

 plant life, as it exists under the alternating influence of solar 

 light and darkness ; he investigates with astonishing precision 

 and minuteness their natural movements of circumnutation and 

 nightly or nyctitropic action, but does not extend his inquiries 

 to the conditions resulting from continuous light. He clearly 

 proves that nyctitropic action is instituted to protect the delicate 

 leaf-cells of plants from refrigeration by radiition into space, 

 but it does not follow, I would submit, that this protecting 

 power involves the necessity of the hurtful influence. May it 

 not rather be inferred from Dr. Darw in's investigations that the 

 absence of light during night-time involved a difficulty to plant 

 life that had to be met by special motor organs, which latter 

 would perhaps be gradually dispensed with by plants if exposed 

 to continual ligh' for some years or generations? 



It is with great diffidence, a' d with ut wishing to generalise, that 

 I feel bound to state as the re-ultof allmy experiments, extending 

 now over two winters, that although periodic darkness evidently 

 favours growth in the sense of elongating the stalks of jlants, 

 the continuous stimulus of lii;ht appears favourable for healthy 

 development at a greatly accelerated pace, Ihr u^h all the stages 

 of the annual life of the plant, from the early leaf to the 

 ripened fruit. The latter is superior in size, in aroma, and in 

 colour to that produced by alternating light, and the resulting 

 seeds are not at any rate devoid of regerminating power. 



Further experiments are neces ary, I am aware, before it 

 would be safe to generalise, nor does this question of diurnal 

 rest in any way bear Ujon that of annual or iv inter rest, which 

 probably most plants, that are not so-called annuals, do require. 



The beneficial influence of the electric light has been very 

 manifest upon a banana palm, which at two ]5eriods of its 

 existence, viz., during its early growth and at the time of the 

 fiuit development, was placed (in February and March of 1880 

 and 1881) under the night action of one of the electric lights, 

 set behind glass at a distance not exceeding two yards from the 

 plant ; the result was a bunch of fruit weighing 75 pounds, each 

 banana being of unusual size, and pronounced by competent 

 judges to be unsurpassed in flavour. Melons .ilso, remarkable 

 for siz; and aromatic flavour, have been produced under the 

 influence of continuous light in the early spring of iSSo and 

 1881, and I am confident that still better results may be realised 

 when the lest conditions of temperature and of proximity to the 

 electric light have been thoroughly investigated. 



My object hitherto has rather been to ascertain the general 

 condi ions necessary to promote growth by the aid of electric 

 light than the production of quantitative results ; but I am 

 disposed to think that the time is not far distant when the 

 electric light will be found a valuable adjunct to the means at 

 the disposal of the horticulturist, in making him really indepen- 



