72 HOW CROPS GROW. 



tion of the flaxsecd. The external cells, a, contain the mucilage. When 

 soaked in water, the mucilage swells, bursts the cells, and exudes. 



One or other of these kinds of gum has been found in 

 the following plants, viz., basswood, elm, apple, grape, 

 castor-oil bean, mangold, tea, sunflower, pepper, in various 

 sea-weeds, and in the seeds of wheat, rye; barley, oats, 

 maize, rice, buckwheat, and millet. 



In the bread-grains, Arabin, or at least a soluble gum, 

 occurs often in considerable proportion. 



TABLE OP THE PROPORTIONS (per Cent) OP GUM IN VARIOUS AIR-DRY 

 PLANTS OR PARTS OF PLANTS. 



(According to VonBibra, Die Getreidearten und das Brad.) 



Wheat kernel 4.50 



Wheat flour, superfine 6.25 



Spelt flour, (Triticum spelta,} 2.48 



Wheat bran 8.85 



Spelt bran 12.52 



Rye kernel 4.10 



Rye flour ' 7.25 



Rye bran 10.40 



Barley flour 6.33 



Barley bran 6.88 



Oat meal 3.50 



Rice flour 2.00 



Millet flour 10.60 



Maize meal 3.05 



Buckwheat flour 2.85 



The gums are converted into sugar by long boiling with 

 dilute acids. 



The recent experiments of Grouven show that, contrary 

 to what has been taught hitherto, gum, (at least gum 

 Arabic,) is digestible by domestic animals. 



Saccharose or Cane Sugar, C 12 H 22 O u , so called be- 

 cause first and chiefly prepared from the 

 sugar cane, is the ordinary sugar of com- 

 merce. When pure, it is a white solid, 

 readily soluble in water, forming a color- Fi 



less, ropy, and intensely sweet solution. It crystallizes in 

 rhombic prisms, fig. 14, which are usually small, as in 



