214 CONVERSION OF STARCH INTO SUGAR. 



the starch of Potatoes and other tubers, is converted, when re- 

 quired for the nourishment of the growing buds, into sugar, 

 which is absorbed by their vessels ; and nearly the same may 

 probably be said of every other instance, in which starch is laid 

 up for a purpose of this kind. 



341. Now this change of starch into sugar is one of a purely 

 chemical nature ; for it can be performed in the laboratory of the 

 chemist, by pouring hot water on the starch, so as to break the 

 vesicles and set free the contained gum ; and then treating this 

 with a weak acid for some time ; by which the whole is converted 

 into a sugar, that scarcely differs from that of other kinds. In 

 the Vegetable economy, however, this change is effected by 

 another means. In the juices of the plants themselves, there is 

 a substance termed diastase; very minute quantities of which, 

 have the remarkable property of changing starch into sugar. 

 This diastase exists in seeds, and is found in larger quantities 

 near the eyes or young buds of the Potato, by the vessels of which 

 it is carried through the mass of starch when required. How 

 beautiful an arrangement it is, that a substance possessed of the 

 remarkable property of converting starch into sugar, should be 

 formed, wherever a store of the first of these substances is laid 

 up, for the purpose of affording a supply of the second when re- 

 quired, and that this diastase should be found nowhere else, 

 than in the very parts of the vegetable structure, in which it will 

 be of use ! 



342. We see, then, that the form in which nourishment is 

 conveyed to the growing parts of plants, is that of gum or sugar. 

 These two substances are composed of the same elements, in 

 nearly the same proportion ; and the former may be changed 

 into the latter. They are usually found together in the cambium 

 (. 329), which is destined to be gradually organised, or con- 

 verted into tissue ; and also in that thick mucilaginous* fluid, 

 which forms the pulp of the very young seeds, that exist in the 

 seed-vessel before the flower has fully expanded. The gum- 

 miness of this fluid is at once perceived by its glutinous proper- 

 ties ; and that it contains sugar, is known by the sweetness of 



* Mucilage is the term applied to a solution of gum in water. 



