May 29, 1866. ] 



JOUBNAL OF HOETICULTURE AND COTTAGE GARDENER. 



399 



pxclndmg the lipbt. in order io obtain complete darkness, and to 

 diminiEh the influence of the variations of temperature when light 

 was not required. By sinkinK it in the ^Tound, liy the tliickness of 

 its walls, and bv the covering of its exterior surfaces with straw, 

 mats, ifcc, the same fixed degree of temperature could be obtaiued 

 as in a cellnr. The vaulted bailding should have an nnderground 

 .communication with a chamber containing the heating and the 

 electrical apparatus. The entrance into the experimental hot- 

 honse should be through a passage closed by a scries of successive 

 doors. The temperature should be regulated by metallic con- 

 ductors, heated or cooled at a distance. Kngineers have already 

 devised means by which the temperature of a room, acting on a 

 valve, regulates the entry or exit of a certain amount of air, so 

 that the heat regulates itself.* Uso conld be made of sncU an 

 apparatus when necessary. 



Obviously, with a hothouse thus constructed, the growth of 

 plants conld be followed from their germination to the ripening of 

 their seeds, nnder the inflnence of a temperature and an amount of 

 light perfectly definite in inten.sity. It could then be ascertained 

 how heat acts daring the successive phases from sowing to 

 germination, from germination to flowering, and from this on to 

 ihe ripening of the seed. For different species various curves 

 conld be constructed to express the action of heat on each function, 

 and of which there are already some in illustration of the most 

 .simple phenomena, such as germination. + the growth of stems, and 

 the course of the sap in the interior of certain cells.; We should be 

 able to fix a great number of those minima and maxima of tempera- 

 ture which limit physiological phenomena. Indeed, a question 

 more complicated might be investigated, towards the solution of 

 which science has already made some advances — namely, that of 

 the action of variable temperature ; and it might be seen, if, as 

 appears to be the case, these temperatures are sometimes beneficial, 

 at other times injurious, according to the species, the function in- 

 vestigated, and the range of temoerature. The action of light on 

 vegetation has given rise to the most ingenious experiments. Un- 

 fortunately, these experiments have sometimes ended in coutra- 

 ilictory aiid uncertain results. The best ascertained facts are. the 

 importance of sunlight for the development of the green colouring 

 matter, the decomposition of cai-bonic acid gas by the foliage, and 

 certain phenomena relating to the direction or position of stems 

 and leaves. There remains mnch yet to learn upon the effect of 

 diffused light, the combination of time and light, and the relative 

 importance of light and heat. Does a prolonged light of several 

 days or weeks, such as occurs in the Polar Regions, produce in 

 exhalation of oxvgen. and in the fixing of green matter, as much 

 effect as the light" distribnted from twelve to twelve hours, as at the 

 Equator? No one knows. In this case, as for temperature, 

 curves should be constructed, showing the increasing or diminish- 

 ing action of light on the performance of each function ; and as 

 the electric light resembles that of the sun. we could in our experi- 

 mental hothouse submit vegetation to a continued light. 3 



A building such as I propose would allow of light being passed 

 through coloured glasses or coloured solutions, and so prove the 

 effect of the different visible or invisible rays which enter into 

 the composition of sunlight. For the sake of exactness nothing is 

 superior to the decomposition of the luminous rays by a prism, 

 and the fixing the rays by means of a heliostat. Nevertheless, a 

 judicious selection of colouring matters, and a logical method of 

 ■performing our experiments, wiU lead to good results. I will give 

 as proof, that the recent most careful experiments concerning the 

 action of various rays upon the production of oxygen by leaves, 

 and upon the production of the green colouring matter, have only 

 confirmed the discoveries made in 1836, without either prism or 

 heliostat. by Professor Daubeny,' from which it appears that the most 

 luminous rays have the most power, next to them the hottest rays, 

 and lastlv those called chemical. 



Dr. Gardner in 1S43, Mr. Draper immediately after, and Dr. C. 

 M. Gmllemin in 1857,1; corroborated by means of the prism and 



• See the electric apparatus of M. Carbonnier, exhibited at Chiswick in 

 1857, figured in the " Flore cles Serres et Jardins," vol. xii. Jliscell. p. 184. 



+ Germination under different degrees of constant heat, by .Mph. de 

 CandoUe, in the ••BibUotbOque Univcrselle de Geneve" (Archives des 

 -Sciences , November, 1865. 



; If the curves have not been constructed, the data for their construc- 

 tion are, at least, dispersed throughout our books. I will cite, for instance, 

 the growth of a scape of Dasvlirion, as observed by M. Ed. Morren 

 (" Bclgique Horticole," 1865, p. 822). The flgnres there given are not favour- 

 .able to the accepted notion, that the growth of tissues is more active by 

 night than by day. . .... 



i The apparatus which produces the most persistent and vivid light is 

 the magneto-electric machine, based on the development of induction by 

 magnetism, as discovered by the illustrious Faraday. The galvanic pile 

 is replaced bv a steam-engine of low power, which sets in motion a wheel 

 furnished with magnets ("Bibl. Univ. de Gemve, Archives Scientif.,1861, 

 V. 10, p. 160."). The working of this machine is inexpensive ; but unfortu- 

 nately, the magnets are very costlv. This svstom has already been applied 

 to two lighthouses— that "at the" South "Foreland, and to that of the 

 "Societe I'Alhance," at Havre— in consequence of the experiments of 

 MM. E. Becquerel and Tresca. 



J Daubeny. " Philos. Trans.," iaS6, part 1. 



H Dr. Gardner. "Eduib. Phil. Mag.," 1844. extract in French m ' La 

 Biblioth. Univ. de Geneve." Februarv, 1844; Draper, " Edinb. Phil. Mag.. 

 September, 1844, extract ib., 1M4, vol. 54 ; Guillemin ^C. M.), "Ann. Sc. 

 Nat.," 1857, ser. 4, vol. 7, p. 154. 



the heliostat the discovery of Dr. Daubeny. which negatived the 

 oitinions prevalent since the time of Senebier aud Tessicr, and 

 which were the result of erroneous* experiments. It was difBcnlt 

 to believe that the most refrangible rays^^olet for instance, 

 which acts the most on metallic boiUes — as in photometrical 

 operations, should be precisely those which have least effect in 

 decomposing the carbonic acid gas in plants, aud have the least 

 effect over the green matter in h;aves. Notwithstanding the con- 

 firmation of all the experiments made by Dr. Daubeny, when 

 repeated by numerous physicists and by more accurate methods, 

 the old opinions, appearing more probable, still influenced many 

 minds, f till Mr. JuHns Sachs, in a series of verj' important 

 experiments again affirmed the truth.; It is really the yellow 

 and orange rays that have the most power, and the blue aud 

 violet rays the least, in the phenomena of vegetable chemistry ; 

 contrary to that which occurs in mineral chemistry, at least in the 

 ease of chloride of silver. The least refrangible rays, such as 

 orange and yellow, have also the twofold and contrary property, 

 such as pertains also to white light, and which produces the 

 green colouring matter of leaves or bleaches them, according to 

 its intensity. It is these, also, which change the colouring matter 

 of flowers when it has been dissolved in water or alcohol. § Those 

 rays called chemical, such as violet, and the invisible rays beyond 

 violet, according to recent experiments, canfirmatory of those of 

 ancient authors — those of Sebastian I'oggioli, in 1817,'' and of 

 C. M. Guillemin — have but one single well-ascertained effect, that 

 of favouring the bending of the stem towards the quarter from 

 which they come more decidedly than do other rays ; yet that is an 

 effect perhaps more negative than positive, if the flexure proceeds, 

 as many still believe, from what is going on on the side least exposed 

 o the light.'" 



The effect upon vegetation of the non-visible calorific rays at the 

 other extremity of the spectrum have been but little studied. Accord- 

 ing to the experiments we have on this subject, they would appear to 

 have hut little power over any of the functions ; but it would be worth 

 whUe to investigate further the calorific regions of the spectrum by 

 emploving Dr. Tyndall's process— that is, by means of iodine dissolved 

 in bisulphide of carbon, which permits no trace of visible light to pass. 



How interesting it would be to make all these laboratory experiments 

 on a large scale ! Instead of looking into small cases, or int.) a small 

 apparatus held in the hand, and in which the plants cannot be well 

 seen, the observer would himself be inside the apparatus, and could 

 arrange the plants as desired. He might observe several species at 

 the same time, plants of all habits, climbing plants, sensitive plants, 

 those with coloured foliage, as well as ordinary plants. The experi- 

 ment might be prolonged as long as desirable, and, probably, unlooked- 

 for results would occur as to the form, or colour of the organs, parti- 

 cularly of the leaves. 



Permit me to recall on this subject an experiment made in 18.53 by 

 Professor \ou Martins." It wiU interest horticulturists now that 

 plants ivith coloured foliage are becoming more and more fashionable. 

 M. "N'on Martins placed some plants of Amaranthus tricolor for two 

 months under glasses of various colours. Under the yellow glass the 

 varied tints of the leaves were all preserved. The red glass rather 

 impeded the development of the leaves, and produced, at the base of 

 the limb, yellow instead of green ; in the middle of the upper surface, 

 yellow instead of reddish-brown, and below, a red spot instead of 

 pnrplish-red. "With the blue glasses, which allowed some green and 

 yellow to pass, that which was red or yellow in the leaf had spread, 

 so that there only remained a green border or edge. Under the nearly 

 pnre violet glasses, the foliage became almost uniformly gieen. Thus, 

 by means of coloured glasses, provided they are not yeUow, horticul- 

 torists may hope to obtain at least temporary effects, as to the colour- 

 ing of variegated foliage. 



The action of electricity on vegetation is so donbtfnl, so difficult to 

 experiment upon, that I dare hardly mention it ; but it can easily be 

 understood how a building constrncted as proposed might facilitate ex- 



• Senebier. " Mim. Phys. et Chim.," 2, p. 69 ; Tessier, Mem Acad. Sc., 

 1783- Gilby "Ann.de Chimie," 1821. v. 17; Succow, " CommenUtio de 

 lucis effectibus chemicis." in, 4to, Jenfi, 1828, p. 61 ; Zantedeschi, cited 

 bv Dutrocbet. Comp. Rend. Acad. Sc. 1844, sem. 1. p. 8o3. 



"t As a proof of the persistence of the old opinion, I will quote a phrase 

 of Professor T>-ndall's in his most clear and interesting treatise "On 

 Radiation." (London, 1865), p. 6 :— " In consequence of their chemical 

 energv, these ultra-violet ravs are of the utmost importance to the organic, 

 world"" I do not know whether the author had in view the mBuence o[ 

 the chemical ravs over the animal kingdom : but, according to certain 

 passages of Mr. "Sachs, 1 doubt if they have more power over ammals 

 than thev have over plants; but Professor Tyndall did not concern him- 

 self with "these questions, he was content to explain admirably the physical 

 nature of the various rays. ..„i,„ 



; The researches of Mr. Sachs first appeared in the "Botanische 

 Zeitnng" thev arc coUectcd and condensed in the remarkable volume 

 called " Handbuch der l*hysiologischen Botanik," vol. 4, Leipsig, 1855, 

 p. 1 to 46. _ io Ao 



J Sir .John HerseheU, " Edinb. Philos. Joum.," January, 1843. 



1 S. Poggioli, "OpuscoU Scientiflci," quoted by Dutrocbet, Compt. Kena 

 Acad. Sc," 1844. sem. 1. p. 850. j j „„ .i,„ 



i: The rather confused an.l questionable explanations, founded on tno 

 notions of Dutrocbet, of the existence of a deoxidising power on the 

 brightest Bide, clash with the fact that the bine, indigo, and violet rays. 

 the least powerful for deoxidising tissues, arc the most powerful m caus- 

 ing them to bend. 



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