VEGETABLE PEODUCTS — GUM. 163 



The quantity of starch remained, the same during the dormant state 

 in winter, but decreased whenever the plant began to grow. 



Starch is stored up in many seeds. It exists in roots, especially 

 in those which are fleshy ; in stems ; in the receptacles of flowers ; 

 and in pulpy fruits. The seed-lobes of the Bean and Pea, and 

 many other leguminous plants ; the roots and the underground stem 

 of Maranta arundinacea (arrow-root), and of Canna coccinea (tous- 

 les-mois), Canna Achiras and 0. edulis ; the stem of Sago Palms (Sagus 

 Rumphii and farinifera), and of the Cycas order ; the receptacle of the 

 artichoke, and the pulp of the apple, are familiar instances of parts in 

 which starch abounds. The grains of potato-starch are of large size, 

 with pearly or sparkling lustre, having one or more hila, and frequently 

 cracks on the surface. Those of arrow-root are small, and have a dull 

 white appearance, while those of tous-les-mois are larger, and glisten 

 like potato-starch. In some cases starch is associated with poisonous 

 or acrid juices, as in Jatropha Manihot, which yields Cassava and 

 Tapioca, and in Arum maculatum, the underground stem of which 

 furnishes Portland sago. Inulin (Cs Hj, 0^) is a substance analogous 

 to starch, to which Iodine communicates a brown colour. It is found 

 in the roots and tubers of Inula Helenium (Elecampane), Dahlia 

 variabilis, and Helianthus tuberosus (Jerusalem artichoke) ; while 

 Lichenin is a variety of starch occurring in Cetraria islandica (Iceland 

 moss). Lichenin or lichen starch consists of C, Hj„ Og, and is de- 

 posited on the primary cell-wall of the plant, in the form of an encrust- 

 ing layer. By the action of malt, or of sulphuric acid upon starch, by 

 long boiling in water, or by heating up to 400° Fahrenheit, a soluble 

 gummy substance is produced called dextrin* (Cg Hj,, 0^), which, when 

 dried, constitutes British gum. It is one of the steps in the process 

 of the conversion of starch into sugar. 



Gum is one of the substances which are produced abundantly in 

 the vegetable kingdom. Its composition is Oj^ H^^ Ojj, the same as 

 that of Cane-sugar. It exists in many seeds, exudes from the stems 

 and twigs of many trees, and is contained in the juices of others from 

 which it does not exude. It is one of the forms through which organic 

 matter passes during the growth of plants. The different kinds of 

 gums have been divided into those which are soluble in eold water 

 (Arabin, mucilage), and those which only swell up into a gelatinous 

 matter (Bassorin or Tragacanth, Cerasin, and Pectin). Arabin is 

 familiarly known by the name of gnm-arabic or gum-senegal, and is 

 the produce of various species of Acacia, chiefly natives of Arabia, 

 Egypt, Nubia, and Senegambia, such as Acacia Ehrenbergii, tortilis, 

 Seyal, arabica, vera, and albida. From the bark of these plants it 

 exudes in the form of a thick juice, which afterwards concretes into 



* Dextrin is so called from possessing the property of effecting the right-handed rotation 

 of the plane of polarisation of a ray of polarised light. 



