94 THE CARBOHYDRATES 



STARCHES. 



The general formula for all substances belonging to this 

 group is (C,;Hi^05)n, which indicates that on hydrolysis they 

 yield hexoses ; for this reason they may be termed hexosanes. 

 The hexoses produced however are different, and the group 

 may therefore be subdivided as under, the basis of the classi- 

 fication being the nature of the sugar. 



(Dextrosanes. — Ordinary starch, Dextrin, Glycogen, Lichenin, Para- 

 dextrane, etc. 

 Levulosanes.— Inulin, Phlein, Graminin, Triticin, Synanthrin, etc. 

 Mannosanes. — Mannane, Paramannane, Mannocellulose. 

 Galactosanes. — Galactane, Paragalactane. 



DEXTROSANES. 

 Starch or Amylum. 



Starch is one of the most widely distributed substances in 

 the vegetable kingdom ; it may be found in green leaves as a 

 temporary reserve of the photosynthetic products ; as a more 

 or less permanent reserve food-material it occurs in seeds and 

 fruits, where it is not infrequently accompanied by other 

 reserves, for instance proteins ; in the vegetative parts, such 

 as tubers, the living cells of the pith, medullary rays, and 

 cortex of roots and stems ; and also in the latex of certain 

 plants, e.g. Euphorbia. When especially stored, the amount 

 of starch may be considerable ; thus in cereals it may form 

 from 50 to 70 per cent of the dry weight of the grains, and 

 in potatoes from 15 to 30 per cent of the dry weight of 

 the tubers. As is well known, starch grains from different 

 sources show much variety in size and shape, and occur in 

 association with plastids, in which, as Schimper demonstrated, 

 they have their origin. 



Many monocotyledonous plants are characterized by the 

 absence of starch, for example Scilla nutans^ Phleuvi pratense, 

 Allium, etc., but in some of these cases starch granules may 

 occur in the guard-cells of the stomates, in the bundle sheath 

 of the leaves, and also in the bulbs at the base of the growing 

 shoots ; further, in certain plants which normally form sugar, 

 e.g., Musa, Hemerocallis, and Muscari, starch will appear 

 when much sugar accumulates. On the other hand, many 



