LESSON 5.] GUMS AND SUGARS. 17 



perm (b), an intermediate layer (c), the gluten cells (d), and the starch 

 cells (e). 



92. It is well known that rice contains very little nutriment, 

 yet a wild species, found abundantly in "Wisconsin, and known as 

 mountain rice, appears to offer an exception to this rule. In a highly 

 magnified view of a section of Oryzopsis asperifolia, or mountain 

 rice (Fig. 23), we see the pericarp (a), of great substance, and filled 

 (apparently) with bordered pores. To this succeeds (b) the episperm, 

 followed by an intermediate layer (c), and beneath this layer the 



-gluten cells (d), as in the Triticum (wheat). Lastly, we find the 

 cells (e) containing the minute corpuscles of starch. 



93. In addition to the microscopical test for starch (hilum and 

 concentric rings), there is a simple chemical test of much impor- 

 tance, i. e., the Tincture of Iodine ; this re-agent has been briefly al- 

 luded to above 



94. If a tissue suspected to contain starch be treated with a mi- 

 nute quantity (the less the better) of this fluid, and starch be present, 

 a beautiful purple color is the immediate result ; by this simple pro- 

 cess a new combination is formed the iodide of starch. Tincture 

 of iodine fails to produce a similar effect upon any other known veg- 

 etable tissue, and hence it may be regarded as an unfailing test of the 

 presence of Fecula. 



95. By the action of malt, or of sulphuric acid, or by long boil- 

 ing in water, a gummy matter is produced from starch called dextrin, 

 or soluble starch. This material is now abundantly used as a cheap 

 and efficacious form of gum for envelopes, postage stamps, &c. By 

 many authors it is supposed that dextrin is formed of the substance 

 contained in the interior of the corpuscles ; at all events, the forma- 

 tion of dextrin is one of the first steps in the conversion of starch 

 into sugar. 



96. GUM is a substance abundantly produced in the vegetable 

 kingdom. It is found in many seeds, exudes from the stems and 

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

 which it does not exude. 



97. The different kinds of gum have been divided into those 

 which are soluble in cold water (gum arabic and mucilage), and those 

 which only swell up into a gelatinous matter (tragacanth, cerasine, 

 and pectine.) 



98. Grum arabic, or gum Senegal, is produced by various species 

 of acacia, chiefly natives of Arabia ; hence its scientific name, gum 

 acacia, or, on the other hand, its common name of gum arabic. 



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