March 2, 1899] 



NA TURE 



41: 



much used in meteorology, but which seems capable of various 

 useful applications. 



In the diagram herewith, the line of ordinates measures mean 

 temperatures of the first quarters at Greenwich, and the line of 

 abscissa those at Chicago. The cross-lines represent averages ; 

 39'7 for Greenwich, 28° 'O for Chicago; and each dot, by its 

 position, indicates the character of a winter (temperature of 

 first quarter) at both places 



The vertical and horizontal scales being alike, one can see 

 by the shape of the diagram how much greater are the variations 

 of winter temperature at Chicago than at Greenwich. 



If we call anything above the average mi/d, and anything 

 below it ceM, we find, on counting the dots in the four divisions, 

 this state of things : — 



Greenwich mild, Chicago mild 

 Greenwich cold, Chicago cold 

 Greenwich mild, Chicago cold 

 Greenwich cold, Chicago mild 





Thus, 21 of those 51 first quarters (say 42 per cent.) were of 

 opposite sign, and 30 of like sign. 



The distribution of dots may suggest other points of interest, 

 on which I need not here enlarge. It would be instructive, I 

 think, to make other comparisons of the same kind. Some 

 time ago Prof. Hann compared the winters (December-February) 

 at Jakobshavn, in the west of Greenland, and Vienna {A/e/. 

 Zeits., March 1890, p. 112), and found a larger proportion of 

 unlike signs than the above — viz. 27 cases, against 15 of like 

 sign. Ai.EX. B. MacDo\v.\i.l. 



DANTE AND THE ACTION OE LIGHT UPON 

 PLANTS. 



T N the history of vegetable physiology, sufificient im- 

 -*- portance has not been given to Dante's observations 

 upon the action of solar light and heat upon plants, and 

 to the ideas upon this action that existed in Italy in the 

 fourteenth century. Sachs, in his " Geschichte der 

 Botanik," ignores Dante and Pier de' Crescenzi com- 

 pletely ; observing in a general way : " Of the importance 

 of Light and Heat for the nourishment and the growth of 

 plants, next to nothing is to be found in the authors that 

 wrote before the last decades of the seventeenth century ; 

 although certainly the action of these agents must have 

 been known from the oldest times, in plant culture and 

 in several special circumstances." ' P. A, Saccardo also, 

 in his " Primato degF Italiani nella Botanica," does not 

 take any notice of the observations and opinions of Dante 

 and of Pier de' Crescenzi on light action. 



In such special works as Ottaviano Targioni Tozzetti's 

 "Cognizioni botaniche di Dante," written in 1820; R. de 

 Visiani's "Accenni alle Scienze botaniche nella Divina 

 Commedia," published in 1865 rand the quite recent book 

 "Dante Georgico," in which, in a complete and able 

 manner, Count Gastone di Mirafiore has collected all the 



^ Sachs, *' Gesch. der Botanik," p. 387. 



NO. I 53 I, VOL. 59] 



references to agriculture, and to plants and animals, that 

 are to be found in the " Divina Commedia" and in the 

 minor works of Dante : the historical importance of some 

 of Dante's observations upon light action has been over- 

 looked ; and no mention is made of the opinions prexalent 

 upon this subject in Dante's time, as given especially by 

 Pier de' Crescenzi.' 



The best-known and often-quoted verses, in which the 

 action of solar radiation upon plants is first noted in a 

 modern language are those of " Purgatorio," xxv. 77 : 

 Guarda il calor del Sol che si fa vino 

 Giunto all' umor che dalla vite cola ; 



or, in Longfellow's translation : 



Behold the Sun's heat which becometh wine 

 Joined to the juice that from the vine distils. 



Dante, despite his remarkable clear-sightedness in 

 noting and describing natural phenomena, was not 

 emancipated from what Whewell calls the comment- 

 atorial spirit of the Middle Ages ; and these verses are 

 but a powerful and poetical rendering of a passage irv 

 Cicero's " De Senectute," a book which, as may be 

 gathered from the several quotations in the " Convivio,'' 

 was much studied by Dante. There is no doubt, how- 

 ever, that Dante's verses have a special interest in the 

 history of vegetable physiology : for they drew attention 

 to the importance of their meaning in two such master 

 minds as Galileo and Francesco Kedi. 



It is not unlikely that the verses of Dante influenced 

 Leonardo da Vinci in believing that "the sun givetb 

 spirit and life to plants, and the soil with its moisture 

 nourisheth them," - leading him to an experiment in which 

 the importance of leaf-function in the nourishment of 

 plants is first noted, two hundred years before Malpighi. 

 In this experiment Leonardo caused a water-fed plant lf> 

 grow prosperously and bear fruit abundantly, although 

 its roots had purposely been reduced to "only one tiny 

 rootlet " {solainente una iiiinima radicc). Leonardo thus- 

 succeeded in causing a plant to grow chiefly by its 

 foliage, to " viverc della n'ma" (" Paradiso," xviii. 29) : an 

 experiment that would have been too dangerous for the 

 experimenter in Dante's days. The "t'/tyvy df//a cima '' 

 was for Dante such a supernatural condition that it could 

 only be described as possible for the symbolical tree of 

 Heaven : 



. . . the tree, whose life 



Is from its top, whose fruit is ever fair. 



And leaf unwithering. 



— Carys Trail slal ion. 



The verses of Dante on the action of sunlight on the 

 vine are paraphrased in new verses in the " Bacco m 

 Toscana" of Redi, the poet and naturalist, in describing 

 the growth of wine, " that lovable blood " : 



Si bel sangue e un raggio acceso 

 Di quel Sol, che in ciel vedete ; 

 E rimase avvinto e preso 

 Di piii grappoli alia rete ; 



or, as rendered in English by C. H. D. Giglioli : 



That blood so fine is a kindled ray 

 From the Sun, in heaven set, 

 Entangled and held a prey 

 By clustering grapes in their net. 



Galileo, as Magalotti tells us, believed that " wine is a 

 compound of light and sap." Magalotti rather diffusely 



1 Ottav. Targioni Tor.KtU, " Delle Cognizioni botaniche di D.intc 

 espresse nella Divina Commedia." Atti dell' Accad. della Crusca. Tomo 

 ii. (Firenze, 1829.) Roberto de Visiani, ''Accenni alle Scienze botaniche 

 nella Divina Commedia" ; in " Dante e il Suo Secolo." (Firenze, 1865.) 

 Gastone di Mirafiore, "Dante Georgico." (Firenze, 189S.) See .tlso : G. 

 Bottagisio, " Osservaz. sopra la Fisica del Poema di Dame." Nuovaediz. 

 sulla prima Veronese del 1807, a cura di G. L. Passerini, Citta di Castello, 



' Work of Leonardo da Vinci." (London, 



