March 



[899] 



NATURE 



419 



forcibly describes these actions in different parts of his 

 poem with well-known verses : 



Quale i fioretti, dal notturno gelo 



Chinati e chiiisi, poi che il Sol gl' imbianca, 



Si drizzan tutti aperti in loro stelo;' 



or, in Gary's translation : 



As florets, by the frosty air of night 



Bent down and clos'd, when day has blanch'd their leaves, 



Rise all unfolded on their spiry stems. 



And in " Paradiso," xxii, 55 : 



Cosi m' ha dilatata niia fidanza, 

 Come il Sol fa la rosa, quando aperta 

 Tanto divien quant' ella ha di possanza ; 

 or : 



Have raised assurance in me : wakening it 

 FuU-blossom'd in my bosom, as a rose 

 Before the sun, when the consummate flower 

 Has spread to utmost amplitude ; 



and more forcibly still in " Purg.," xxxii. 54 : 

 Come le nostre piante, quando casca 

 Giii la gran luce mischiata con quella 

 Che raggia retro alia celeste lasca, 

 Turgide fansi ; e poi si rinnovella 

 Di suo color ciascuna, pria che il Sole 

 Giunga li suoi cor.^ier sott' altra Stella ; 



but not so happily translated by Gary : 



As when large floods of radiance from above 

 Stream, with that radiance mingled, which ascends 

 Next after setting of ihe scaly sign. 

 Our plants then burgein, and each wears anew 

 His wonted colours, ere the sun have yok'd 

 Beneath another star his flamy steeds. 



The action of solar radiation in causing the rise of sap 

 in plants, and in producing what nowadays we call vege- 

 table transpiration, was especially noticed in the time of 

 Dante, four hundred years before the experiments of 

 Guettard. 



Pier de' Crescenzi, the famous agricultural writer 

 of Bologna, was a contemporary of Dante, and he lays 

 special stress on the action of solar heat and light upon 

 plants. Grescenzi's w-ork, the "' Opus Ruralium Com- 

 modoriim," was written in 1305, when the "Divina Gom- 

 media " was not yet finished, and when a part of the 

 "Gonvivio" had not been written. Grescenzi's book, 

 originally written in Latin, became so popular that in the 

 lifetime of the author, or shortly after his death, it was 

 translated into Italian ; and since then, down to the be- 

 ginning of this century, that book (it was among the first 

 books printed, the first edition being of Strassburg, 1471) 

 remained the standard agricultural encyclopaedia, re- 

 published in thirty Italian editions, and translated into 

 the chief languages of Europe. 



It is from Crescenzi that we gather best what Dante's 

 ideas were on the action of light upon plants ; and to 

 Crescenzi we must look as the fountain-head of the ideas 

 prevalent on that subject during many centuries. 

 Crescenzi likened the vegetable to a man planted with 

 his head downwards in the soil and all his limbs in the 

 air. For the roots of a plant were considered the really 

 vital part of the organism, its head and heart in one, by 

 which, with many mouths, the roots sucked up with 

 moisture the food prepared in the soil by the corruption 

 of corruptible things. The soil was for plants what the 

 stomach is to animals. Four hundred years later we 

 still find Linnaeus writing that plantarum venlriculus est 

 terra. According to Crescenzi, not only is solar radi- 

 ation the cause of the sucking-up action of vegetables, 

 but also of the transformation and assimilation of plant 

 food, separating the water with which it is mixed, the 

 water being then transpired away. 



1 'Inferno," ii. 127. 



KO. I 53 I, VOL. 59] 



Thus Crescenzi finds that the growth and ramifying of 

 plants is due to two causes : nourishment from the soil 

 and the action of sunlight : " Branches . . . multiply for 

 two reasons : one of which is material, namely the 

 abundance of nourishment ; and the other is efficient, 

 that is the heat of the sun, which on all sides toucheth 

 the tree, and causeth the sap to boil up, and draweth it 

 forth ; and therefore many branches shoot outwards in 

 the upper parts, where the sap is more straitened, and is 

 rendered more subtle by digestion. And the true proof 

 of this is that plants which are surrounded by many 

 other plants, as happens with trees in thick and shady 

 woods, grow high, and do not produce many branches, 

 nor are their trunks thick, and they have a certain lack 

 and feebleness of branches ; for, by want of sun, their 

 sap is not drawn forth, nor does it boil at their outer ex- 

 tremities ; for the coldness of the shade keeps in the 

 heat which being constrained inside, fleeing from its con- 

 trarj', sendeth on high all the nourishment." ' 



"... The sap is a humour which, through the pores 

 of the roots is attracted to nourish all the plant, and by 

 its nourishing power gets distributed in all the parts of the 

 plant ; and it is necessary that it should be changed to 

 the similitude of the plant by digestive heat." 



"... the nourishing humour of plants is more insipid 

 when in the root, but as it goeth farther and farther from 

 the root, the more it gaineth in taste convenient to the 

 plant ; and in the same way as it gaineth in savour, so 

 doth it gain in density and in subtlety and in acidity ; 

 for by the action of heat these changes must occur. . . ."- 



"... because fruits require much power of the sun, 

 leaves are placed somewhat distant from the fruits, so 

 that these be not in the shade, and the digestion be not 

 prevented that is done by the sun." ^ 



"... the sun's heat giveth, as it were, perfection and 

 form, and nearly giveth life ; for this reason moisture is 

 formed in plants continually." * 



The hardening influence of light upon vegetable 

 tissues, and the favouring of growth by heat in 'the 

 absence of light are, for the first time in the history of 

 plant life, noticed by Crescenzi, who thus shows that he 

 formed some idea of the distinct action upon plants of 

 heat and light : " Plants in warm weather grow in the 

 darkness of night ; and in the heat of the sun they harden 

 and become woody."'' This is a precise and simple 

 statement of facts, without any reference to the action 

 of the moon, as we find in later writers, such as 

 Levinus Lemnius, the celebrated Dutch doctor, in his 

 curious book, " De Occultis Naturje jVIiraculis," published 

 in 1559." _ 



It is by Carradori, at the beginning of this century, 

 that we again find stress laid on the action of light in 

 giving robustness and hardness to vegetable tissues. 

 Indeed, the words of Crescenzi may be paraphrased 

 with those of the most eminent writer on the physiology of 

 plants of our own times : " -So far as plants are concerned,, 

 warmth chiefly signifies growth ; while light, on the 

 other hand, brings about nutrition." "' 



Even as late as Liebig sufficient importance was not 

 given to the action of light in hardening growing tissues ;. 

 and only the experiments of Sachs and of Ludwig Koch 

 have explained to us the reason why thick seeding, or a 

 luxuriant vegetation, is followed by the laying of wheat 

 and other high grasses. 



It is evident that in the days of Dante a new spirit of 

 inquiry was beginning, regarding not only the life of 



1 Per de Crescenzi, " Trattato dell' Agricokur.i," lihr. ii. cap. 5- 



- Id., libr. ii. cap. 4. 3 Id., libr. ii. cap. 6. 



J Id., libr. ii. cap. is. '" Pier dei Crescenzi, libr. xi. cap. 14. _ 



Ii Lemnius writes : " For we see that plants receive nourishment that is 

 moved by the heat of the sun ; and by night this food is diffused so that 

 the food getteth increase ... by day, by virtue of the sun, all things 

 ripen ; and by night, by virtue of the moon, they .are filled with humour 

 and eet swollen. 



!• Julius V. Sachs, " Lectures on the Physiology of Plants,' trans, by 

 H. Marshall Ward (Cvfcrd, 1887), p. 198. 



