44* On the facchartnt Principle of Plants. 



1 5. The red-ftriped or circled roots, v^^of-; rind alio is always of a darker colour, afford 

 fugar indeed; but the fyrup is bad, on account of its talc of the root, which caniiot be removed 

 but by expenfive chemical procefles. The runkelriibes of a white riad and yellow internal 

 part do certainly afford moft fugar, which flioots very readily into large cryftals; but their 

 fyrup being of an extremely difguftiag tafte, is of no ufe, when raw fugar only is made. 

 Even the fugar itfelf, prepared from thefe roots, is not eafily, but with difficulty, cleared of 

 that tafte in the condition of raw fugar, though it certainly difappears in refining. For this 

 reafon, tiiis laft variety of the runkelriibe, that contauis fo much fugar, is not to be totally re- 

 jefted, but is rather profitable in the manufactory of fugar. More efpccially, if not intended 



. to be employed as raw fugar, and if the acquifition of the fyriip be difregarded, 



16. It is fufficiently proved, from the phyfiology of plants, that the matter of light has a 

 great fl>are in the formation of fome of their conftituent parts, as to quality, and confcquently 

 on their mutual proportions. I fhall here mention one or two inftances. 



While afparagus is defended againft the light, it becomes fweet, and of a pleafant tafte j 

 but rf light has aiSted upon it, merely for a fliort time, it lofes its fweetnefs and turns bitter. 



Endive likcwife has a tough, harfli tafted leaf, provided it be expofed to the free adlion 

 of ligbt. On the contrary, when the inner leaves are defended, by tying the outer ones 

 together, they change their colour, which paffes from green to yellow; the firmncfs of 

 their texture is weakened; they become tender, foft, brittle, and full of juice; and their 

 •tafte, which was almoft difgufting, becomes mild and agreeable. All thefe changes produced 

 in the external appearance and flavour of |)lants, by the prefence or abfence of the maitter of 

 4ight, can only originate fiomihc. different modifications^ which this matter of light effe^s 

 either in the nature of their conftituent parts, or in their mutual proportions. 



17. Thefe obfcrvations, depending on rcfults generally known, led me feveral years ago 

 to make expciiments, in order to difcover whether the matter of light contributes in general 

 to the ittcreafe or dtcreafe of any certain conftituent part of plants, principally and exclufively ? 

 whether this aQion have the fame efficacy upon all the parts of plants ? or whether the matter 

 of light does intreafe or diminijh the fame conftituent part of a plant, in its various parts, as 

 rsots, leaves, fruity &cc.i To avoid prolixity, I ftiall not defcribe the feveral experiments 

 I have made for the purpofe of anfwering thefe queftions, either with plants growing in open 

 air, or cultivated in hot-houfes, and more efpecially thofe made with the fugar-cane in the hot- 

 houfe> I ftiall only mention thofe refults which bear any relation to the prefent fubje^, 

 ^ding fuch obfervations, or well-known fa61s, as tend to confirm thofe refults. 



The following are the refults of my refearches : 



(a) That the abfence of light augments the faccharine liquor in almoft all roots, or in 

 the germs arifing from them; that its prefence diminiflies it; and that to (hade the whole 

 furfacc of a piece of ground on which fuch roots are raifed, adds very much to the increafe 

 of their faccharine matter. 



(b) That the matter of light has not the fame efficacy, but rather one of an oppoflte kind, 

 «n the other parts of plants j for inftance, the fruits, the faccharine matter of which is aug- 

 mented 



