134 HOW THE SUGAR IS FORMED IN THE SPROUT, 



from the soil; forms an abundant source from which the whole of the 

 starch, rtindered soluble by the diastase, can be supplied with the ele- 

 ments of the two atoms of water which are necessary to its subsequent 

 conversion into grape sugar 



4°. The diastase is formed when the seed begins to sprout, at the ex- 

 pense of the gluien or vegetable albumen of the seed, but as its true 

 constitution is not yet known, we cannot explain the exact chemical 

 changes by which its production is effected. 



5°. When the true leaf becomes expanded, true wood first appears 

 in sensible quantity. By what action of tlie sun's rays upon the leaf 

 the sugar already in solution in the sap is converted into woody fibre, 

 we cannot explain. The conversion itself is in appearance simple 

 enough, since 



Grape Sugar . . = C12 Hig Oi2» and 



Woody Fibre *. . =Ci2ll3 Og . 



Difference . . . . = H4 O4 ; or the former 



must part with the elements of four atoms of water only, to be prepared 

 for its change into the latter. But the true nature of the molecular* 

 change by which this transformation is brought about, as well as the 

 causes which lead to it and the immediate instruments by which it is 

 effected, are all still mysterious. 



§2. Of the chemical changes which take 'place from the formation of the 

 true leaf to the expansion of the flower. 



When the true leaf is formed the plant has entered upon a new stage 

 of its existence. Up to this time it is nourished almost solely by the 

 food contained in the seed, — it henceforth derives its sustenance from the 

 air and from the soil. The apparent mode of growth is the same, the 

 stem shoots upwards, the roots descend, and they consist essentially of 

 the same chemical substances, but they are no longer formed at the ex- 

 pense of the starch of the seed, and the chemical clianges of which they 

 are the result are entirely different. 



1°. The leaf absorbs carbonic acid in the sunshine, and gives off' ox- 

 ygen in equal bulk.f It is in the light of the sun that plants increase in 

 size — their growth, therefore, is intimately connected with this absorp- 

 tion of carbonic acid. 



If carbonic acid be absorbed by the leaf and the whole of its oxygen 

 given off* again, t carbon alone is added to the plant by this function of 

 the leaf. But it is added in the presence of the water of the sap, and 

 thus is enabled by uniting with it to form, as it may he directed, or as 

 may be necessary, any one of those numerous compounds which may 



* All bodies are supposed to consist of particles or moZecMZes of exceeding minuteness, 

 and all chemical changes wliicli tiike place in the same mass of matter are supposed to be 

 owing to the different" ways in which these [)articles arrange themselves. We may form a 

 remote idea of the way in which different positions of the same particles may produce dif- 

 ferent substances, by considering how different figures in Mosaic may be produced by dif- 

 ferent arrangements of tlie same number of equal and similar fragments of various colours. 



t Such \s sensibly the result of experiment. How far this result can be considered as uni- 

 versally true, will be examined hereafter 



X It will be recollected that carbonic acid contains its own bulk of oxygen gas : if, therefrre, 

 the leafgiveotf tiie same bulk of oxygen as:« absorbs of carbonic acid, the result must bi a^ 

 stated in the text. 



