Dr Alison on the Principle of Vital Affinity. 287 



various plants when the fluids from the soil are ascending 

 and dissolving the starch which had been formed and stored 

 up by the living actions of the preceding year ; it appears in 

 almost exactly the same circumstances during the germina- 

 tion of seeds, and in both these cases is useful, as giving a 

 greater degree of solubility to the starch whence it is formed. 

 In both cases it disappears, and probably is converted into 

 some of the varieties of starch, as the vital actions of the 

 plant become more vigorous. Its composition, in its dif- 

 ferent varieties, as given by most analysts, C12 Hn Oji, Cio 

 Hio Oio. or even C12 Hu Ou, denotes that if it be formed 

 from the starch, C12 Hjo 0^^ it must be either by the ad- 

 dition of the elements of water, or by the abstraction of car- 

 bon ; and as its formation, during the germination of seeds, 

 is attended with evolution of carbonic acid, it seems most 

 probable that, in that case at least, it is formed in this last 

 way, under the influence of the oxygen of the air. It appears 

 again in the nectaries of flowers, and in the ripening of fruits, 

 as one of the latest results of the vital action of plants, in 

 those parts of them which are fully exposed to air and light, 

 but at a time when we may reasonably suppose that the vital 

 affinities are becoming comparatively ineff'ective, and when 

 carbonic acid is again evolved. It may be formed by the 

 chemist from some of the varieties of starch by a kind of fer- 

 mentation, excited by diastase, as in malting; or by a cata- 

 lytic action of sulphuric acid ; and it is formed from starch 

 merely by the agency of cold, as in frozen potatoes, and from 

 inuline merely by continued boiling in water ; so that its for- 

 mation from starch in vegetables seems to be most probably 

 a simple chemical change, not the eff*ect of a vital affinity. 

 Farther, it is a compound which takes the crystalline form, 

 essentially diff'erent from any form assumed by those parts 

 of organized structures which exhibit truly vital phenomena, 

 and retains its properties when exposed to air and water bet- 

 ter than any of the matters of which organized forms are 

 composed. From all these facts it may be inferred, with 

 great probability, that sugar, as it appears in the living ve- 

 getable, is generally to be regarded as a first product of de- 

 composition of starch, by the agency of water, and of the 



