4i8 



NATURE 



[March 2, 1899 



dwells on Galileo's opinion. Starting from Castelli's 

 explanation of how a black surface gets more heated in 

 the sun than a white surface, Magalotti evidently believing^ 

 the sun's action to be specially powerful on the \ine, tries 

 to show how light, "that last subtle impalpable dust of 

 bodies," must be especially entrapped by the ripening 

 grapes, and thus become the cause of fermentation and 

 of the strength and aroma of wine.' (jiuseppe Del I'apa, 

 also a contemporary of Kedi, one of the first to experi- 

 ment on vinous fermentation, and to attempt measuring 

 the heat developed in this process, was also of opinion 

 (and he quotes the authority of Dante), that " both oil and 

 •wine " are formed by the action of solar light and heat 

 upon the water contained in plants. Del Papa describes 

 the highly penetrative action of light : " .So subtle that 

 it penetrates in every part of our body without causing 

 ^sensation ; but only by acting inside the eyes does light 

 awaken that feeling w liich we call sight." - 



Indeed, Newton's theory confirmed the opmion that 

 light may enter into combination with matter. And the 

 action of light upon plants was accounted, before and 

 after the experiments of Ingen Housz, by Lavoisier, 

 Senebier, Carradori and others, as a fixing or combining 

 of light in living vegetable substances, the green colour- 

 ing matter being the first product of this combination. 

 " Experiments made on vegetation lead us to believe that 

 light gets combined with some part of the plant, and that 

 to this combination are due the green colour of leaves, and 

 the various colours of flowers . . ." Thus wrote Laxoisier 

 in 1789.^ Senebier, who in 1788 had already noted and 

 experimented upon the antiseptic action of light, ac- 

 counted for this action by believing that light became in 

 some way fixed upon the organic substances that are 

 preserved from decomposition.^ 



When heat and light were no longer regarded as due 

 to corpuscular emission, but as caused by vibrations of 

 the luniiniferous ether, the Dantesque notion of the 

 fixation of solar heat and light died away, or rather 

 became transformed into the notion of the storing up 

 of energy. 



An original observation by Dante is that light is the 

 cause not only of the production of the green colouring 

 matter of plants, but also of its decoloration. In a 

 similitude describing the rise and wane of worldly fame, 

 JJante writes ("Purg.," xi. 115) : 



La vostra nominanza e color d' erba, 

 Che viene e va ; e quel la discolora, 

 Per cui ell 'esce della terra acerba : 



or, in H. T. Cary's translation : 



^ our renown 

 Is as Ihe herb, whose hue doth come and go ; 

 And his might withers it, by whom it sprang 

 Crude from the lap of earth. 



It has been of course a matter of ancient and 

 common observation that the green of vegetation is pro- 

 duced through the action of the sun, and that the sun 

 withers up all vegetation, causing it to fade and dry. 

 But Dante is the first to express the double action of 

 light on the green colouring matter, causing both the pro- 

 duction and the bleaching of the " color d' erba." One 

 fancies him observing the rapid bleaching of green sea- 

 weed and of other fresh vegetaljle matter in the sunlight, 

 and distinguishing between the discolouring and the 

 shrivelling action of the solar rays. 



1 L. M.igalotti. '* Lcltcrc Scientiliclic ed Erudite" (Venezia, 1740), I^l- 

 Ccra V. See also Rcdi's observations in 1686 on this letter : F. Redi, 

 " Operc. (Napoli, 1778), Tomo v. p. 134. 



- Uius. Det Papa, •' Trattali v.irl fatll in diverse Occasioni " (Firenie, 

 '7J4). p. 58 ; and '• Delia Natura dell' Umido e del Secco(Firenze, 1690), 



•' '?*■ 



^ l^voisier, " Trail* de Chimie, present* dans un ordre nouveau el 

 ♦I'apres les d£couverles modcrncs" (Paris, 1789). i. p. aoi. 



* J. Senebier, "Exp sur I'Aclion dela Lumiire Solairc " (< lenive, 1788), 



NO. I 531, VOL. 59] 



We must come down to 1686, to find again observations 

 on the action of light on the production of the green colour- 

 ing matter in plants. John Ray then distinguished be- 

 tween the heat-action and the light-action of the solar 

 rays, observing that the colouring of foliage cannot be 

 due to heat, often greater in closed dark spaces than in 

 the open, but to the light of the sun.' 



Xo exact observation upon the properties of the green 

 colouring matter of plants could be made before a way 

 was found of extracting the colouring principle from the 

 vegetable tissues. This was first done, using alcohol 

 and ether, by the two brothers Guillaume and Hilaire 

 Rouelle, towards the middle of the eighteenth century ; 

 Hilaire Rouelle, the younger brother, published a note on 

 the subject in 1773, remarking on the unstable properties 

 of the green extract of plants. In 1782, Senebier had 

 already shown that the decoloration of this green extract, 

 prepared either with alcohol, or ether, or essential oils, is 

 due to the action of light, and not of heat, and that the dis- 

 appearing of the green colour is connected with a process 

 of oxidation. The first experiments on the decomposi- 

 tion of the green colouring matter in the lix ing plant are 

 due to Gioacchino Carradori, in 1809.- Thus the observ- 

 ation of Dante, in the beginning of the fourteenth cen- 

 tury, on the double action of light in producing and 

 decomposing the green colouring matter in living plants, 

 forestalls a discovery that was made in our century ; and 

 that has been further extended by the recent researches 

 of N. Pringsheim. 



Dante connected in a special way the vegetable activity 

 of plants with the green of their foliage ; and the effect 

 of the sjjecific \ irtue of the soul upon the body is com- 

 pared to the green of leaves, the eftcct of vegetable 

 life : 



Come per verdi fronde in pianta vita ^ 



.\nd Dante observes that the discolouring of leaves is the 

 sign of sickness in plants, in the vine especially (already 

 subject to many maladies in Dante's time, as Crescenzi 

 teaches us\ remarking that the vineyard 



Soon turns 

 To wan and withered, if not tended well ; 



well noting, in the word imbianca, the chlorotic change 

 in the plant : 



la vigna 

 Che toslo imbianca, se il vignaio e reo.* 



No one before Dante, nor for many centuries after 

 Dante, has so well noticed the deprcs>i\e efl'ect upon 

 vegetable life of defective sunlight and persistent rain, by 

 which roots are made to rot in the drenched soil, while 

 leaves become discoloured and fall, and fruit fails to reach 

 maturity : 



lien fiorisce negli uomini il volere ; 



Ma la pioggia continua converte 



III bozzacchioni le susinc vere ; 



or, according to Cary : 



The will in man 

 Bears goodly blossoms ; but its ruddy promise 

 Is by the dripping of perpetual rain. 

 Made mere abortion.' 



The best comment upon the botany of these verses, 

 not well rendered in the English version, is in the recent 

 experiments of Julius Wiesner, on the effect of continual 

 rain upon different kinds of plants. 



The action of sunlight in causing flowers to "awake" 

 and to open was especially remarked by Dante, for he 



• Joa. Raius, " Hi»toria Plantarum," (Ixjndini, 16S6), vol. i. libr. i. p. 15- 



2 G. Carradori, " Sopra la dislruzione del color vcrde operata dalla luce 



in alcuni Vcgctabili viventi," GiornaU di J^isUa lii /irugnateiti, vol. iii. 



I 



» " Purg .■ 

 * •• Paradi^ 

 » "Pjiradi! 



. Cary's Iranslalion 

 124. Cary's Translation. 



