F2 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 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.) 
Wihieat “mernel cia cicis« as rersrate alse ee eee 4.50 
Wheat flour, superfine...........0.-ee00s 6.25 
Spelt flour, (Triticum spelta,)...........24- 2.48 
Wiheat ‘brani. cto. soe civic cieislassarcte elonieletemenate 8.85 
Speltrbram\.. 5.) Jcect see acieieiscls aes aleriete oMteee 12.52 
RY CARCLNCL 55.2 iie tale c’eretersieies = clsemieltia cette 4.10 
Rye MOU... oa cictee saendoC sadsanc Appoo oso 7.25 
BR Y'6 TAM 5 ciec'5" velosci cts oes aveloisce'e!clele(erele eateries 10.40 
C Barley flour...... alale sis Wielete: ove wickets neteeees . 6.33 
ATIC Yi DIAD 2s \cicteve ciesere: «16. n(ese 010 io elise oisisleerere 6.88 
aM CA) Voice eral castes cercslecese Solateteteteiers 3.50 
ICS MLOUT 7 i. s\etsrelele © grasa eialeveie olciete Caeveheiatane 2.00 
Millet flour...... aietayalelaie stale iciovelsisie ini 10.60 
Maize Smeal ciciccre we oieleieicie,oslelelae eiontele a etate 3.05 
Buckwheat flour..... aiele'n, 6 -oretatels bo eRereeas .- 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 
thombie prisms, fig. 14, which gre usually small, as in 
