March ii, 1880] 



NATURE 



439 



a mechanical control. When grown in badly lighted 

 places plants become elongated or " drawn up," while 

 when freely illuminated, the rays of high refrangibility 

 moderate this undue growth in length. Plants also, as 

 is well known, bend towards a source of light ; this is 

 caused by the growth of their stems being checked on 

 the illuminated side, which become consequently shorter. 

 If they are grown behind red glass they are indifferent 

 to one-sided illumination, because the rays which would 

 affect their growth unequally are cut off. Herve'-Mangon 

 showed that this heliotropic effect could be produced by 

 the electric light as well as by that of the sun, and this 

 was a fresh point gained. 



In 1866 Wolkoflf found that seedlings of cress grown in 

 the dark became green after eight hours' exposure to the 

 flame of a Bunsen burner made luminous by sodium 

 carbonate. This was a crucial experiment as far as 

 showing that the production of chlorophyll was inde- 

 pendent of the so-called chemical rays of the spectrum. A 

 few years later Prillieux completed the demonstration of 

 the competence of light from artificial sources to perform 

 all that the sun could do as regards the dissociation of 

 carbon-dioxide by showing in M. Jamin's laboratory at 

 the Sorbonne that oxygen was evolved by a water plant 

 whether illuminated by the electric light produced by a 

 magneto-electric machine, the Drummond light, or even 

 gas-light of sufficient intensity. 



This is the point at which the subject has reirnined f:r 

 Dr. Siemens to take it up. He has worked on a far 

 larger scale than is possible in a laboratory experiment, 

 and has substituted for the sun a little sun of his own. 

 To quote the account in the Times, "an electric centre of 

 light equal to 1,400 candles placed at a distance of two 

 metres from growing plants appeared to be equal to 

 average daylight at this season of the year.'' As far as 

 the experiments went, not merely were all the effects 

 which from a horticultural point of view might be ex- 

 pected from daylight reproduced by the electric light, but, 

 by making the latter supplement the former, double work 

 was extracted from the plants, and the growth of vegeta- 

 tion under the prolonged summer of northern latitudes 

 was artificially imitated. The observation of Herve'- 

 Mangon was also extended, and it was found that the 

 electric light was competent to produce all the mechanical 

 effects of daylight such as bringing about the re-erection 

 of the foliage of plants which during night-time exhibit 

 the phenomenon of sleep. Seedlings of mustard which 

 had never seen daylight were quite as green and vigorous 

 as those which had never been submitted to the artificial 

 light. The same result was shown by the foliage of 

 carrots and those which had been illuminated naturally 

 by day and artificially by night had leaves which were 

 palpably taller and greener than those which, whether from 

 natural or artificial sources, had only enjoyed a smaller 

 amount of illumination. Dr. Siemens promises a more 

 extended series of experiments, and, to give the matter a 

 complete trial, it would certainly be desirable to compare 

 the results during longer periods of growth when the plants 

 were more thoroughly thrown on their own resources. 

 It must be remembered that seedlings grow to a large 

 extent at the expense of the materials stored up in the 

 seeds, and the same thing is true of the foliage produced 

 from fleshy roots like those of the carrot. In both cases 



the plant is mainly feeding on itself. The real test would 

 be to take some short-lived annual and see if it would 

 run through its course with illumination from an artificial 

 source alone, and how the actual weight of plant-tissue 

 manufactured would compare with that produced under 

 an equivalent exposure to sunlight. 



With regard to the action of artificial light on flowers, 

 some caution is requisite in drawing conclusions. The 

 Daily News of March 6 states that " Dr. Siemens ex- 

 hibited to his audience a pot of tulips in bud, which the 

 electric light brought into full bloom in so:v.e three- 

 quarters of an hour." This sounds almost as wonderful 

 as the mango-trick of the Indian jugglers. As a matter 

 of fact the tulips were not, properly speaking, in bud ; 

 the flowers were fully developed, and were simply unex- 

 pand^d, and all that they did when exposed to the electric 

 light they would equally have done in the dark if exposed 

 to a temperature as high as that in the immediate vicinity 

 of the lamp. It is well known that the flowers of tulips 

 are very sensible in this respect to even small changes of 

 temperature, and the heat given off by the lamp used by 

 Dr. Siemens is so considerable that he proposes, as one 

 advantage of its use in horticulture, to employ it " to 

 counteract the effect of night frost," and " to promote the 

 setting and ripening of fruit in the open air." Dr. Siemens 

 also showed a fully developed rose produced under the 

 influence of the electric light, which compared strikingly 

 with an unopened bud which had not bad the same 

 advantage. It might be sugge-.ted that here again the 

 influence of temperature would require to be carefully 

 eliminated. Sachs has found that, \ r. vided the foliage 

 of plants is fully exposed to daylig] t, the flowers will be 

 perfectly developed and will even mature seed in total 

 darkness. And in the case of bulbs when the reserve of 

 nutriment required for the evolution of ilowers is already 

 prepared, with proper conditions of temperature and 

 moisture, the flowers will also be developed in the total 

 absence of light. Eve.i in woody plants this may be ac- 

 complished ; the white lilac which is used for bouquets in 

 the spring, is supplied from bushes of the ordinary kind, 

 which are dug up in the autumn and forced the following 

 yc.rin perfectly dark buildings. The only difference 

 which ever appears to occur is illustrated in this particular 

 instance in the non-development of the colour of the 

 flowers. 



What may be the practical applications of the electric 

 light in horticulture is still a question for the future. Dr. 

 Siemens finds that illumination by it enables plants to 

 sustain increased stove-heat without collapsing. This is 

 an interesting point, because it brings out clearly the 

 mode in which plants arc naturally adjusted to exposure 

 to sunlight without suffering injury. Light increases 

 transpiration, and transpiration prevents the temperature 

 of plant tissues rising to a point at which they would 

 suffer from "scorching." The hope that the electric 

 light might aid investigation as to the mode of formation 

 of alkaloids such as quinine in the plant will scarcely 

 perhaps lead to any practical result. The researches of 

 Howard, on the one hand, show that the Cinchona alka- 

 loids are not formed in the leaves, and making their 

 appearance as they do in the bark, which is progressively 

 thrown off by desquamation, they may with reason be 

 regarded as excretions by which the plant gets rid of 



