368 CHANGES OF OEGANIC MATTER IN THE PLANT. 



that at certain points during its course this solution may tran- 

 siently exhibit more or less fine-grained starch. The tendency 

 of starch to form in this way is "\-ery remarkable in the process 

 of germination. 



930. Inulin. This substance is dissolved in cell-sap (see 183), 

 but is easily separated from it upon immersion of the plant sec- 

 tions in alcohol. It replaces starch in the roots and root-like 

 stems of many perennials belonging to the following orders, — 

 Liguliflorse (Compositae), Campanulaceae, and Lobeliaceee. 



937. Ziicheiiin is abundant in certain lichens, amounting in 

 Cetraria Islandica to more than 40 per cent. 



938. Dextrin. Under tliis name are comprised at least two 

 sulistances^ wliich are produced during the transformation of 

 starch into sugar. Dextrin occurs in the .young sprouts of 

 potato, in most bulbs as they are starting, and in the spring sap 

 of many trees. 



939. The Gums. These are amorphous substances which 

 either dissolve in water or merely swell in it to form soft masses 

 or thick viscous liquids. An example is 



Arabin (2C„H„,0j-|-H^0), the chief constituent of Gum Arabic, 

 obtained from a species of Acacia. It is found associated with 

 arabio acid, which is supposed to be combined with calcium. It 

 occurs in cheriy-tree gum, and to a slight amount in the gum of 

 manj- other plants. 



Of those gums which do not trul^- dissolve, must be mentioned 

 Cerasin, abounding in cherry-tree gum ; Bassorin, or the essen- 

 tial constituent of gum-tragacanth ; and Vegetable Mucus, which 

 occurs in the seed-coats of flax, the pseudo-bulbs of many or- 

 chids, and the leaves of some mallows. 



940. The I'ectin Bodies. According to Freinj- these are 

 derivatives from pectose, a neutral insoluble substance found 

 in unripe fruits and in some flesli^' roots. Pectose undergoes 

 various changes not yet understood. Vegetable jelly, obtained 

 by boiling subacid fruits, is a familiar example of one of the 

 products of such changes. 



941. The sugar group. The more common members of this 

 group are grape-sugar, fruit-sugar, and cane-sugar. The em- 

 pirical formulas of these substances have simple relations, ex- 

 hibited in the following table, in which the}' are compared with 

 that of starch : — 



1 For an account of the allied substances, amylodextrin and achroodextrin, 

 see W. Nageli, Beltrage zur uaheren Kenntniss dev Starkegruppe, 1874. 



