72 HOW CROPS GROW. 
tion of the flaxseed. 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 OF THE PROPORTIONS (per cent) OF GUM IN VARIOUS AIR-DRY 
PLANTS OR PARTS OF PLANTS. 
(According to Von Bibra, Die Getreidearten und das Brod.) 
Wheat kernel...... eer ee te re 4.50 
Wheat flour, superfine............-.e006 . 6.25 
Spelt flour, (Triticum spelta,)........0.06+ 2.48 
Wheat bran........cseeeee aiseinia' bts Sova cketyave . 8.85 
Spelt Dian swasasveacwees tema veered semway vs 12.52 
Rye KEP els e2seveemawaidew i ruwrc inne. vee 4.10 
RYt NOW cvs vs 0xs vxrnwaiaw en vinx ékawes pare 7.25 
RC Dra isc deicnaneeovas Awieie scan sd ameareteis 10.40 
Harley DOU sss seven ewes neassecen ewes ee 6.33 
BAC Y: OTA. raid ceaissvasg gosta Garoueasssin sinners 6.88 
Oat: Meal. co sisiceis nes cease leiats § aMeWia etbvolsreiets 3.50 
RCS MOUP. csiicrscis sae S swinle va ctsin aise Ris aise 2.00 
Millet flour... .ccccssecsesees oie) Se wis aes weave 10.60 
Maize: mealsccviisesaee sere saan ses ‘eens 8,05 
Buckwheat flour..............000: a siacaaied 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,, H,, O,,, 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- Fig. 14. 
less, ropy, and intensely sweet solution. It crystallizes in 
rhombic prisms, fig. 14, which are usually small, as in 
