62 



HOW CROPS GROW. 



corn and barley husks, contain 6 to 30 per cent of a sub- 

 stance insoluble in cold water, but readily taken up in 

 cold solution of caustic soda. On adding to the solution 

 an acid, and afterwards alcohol, a bulky white substance 

 separates, which may be obtained dry as a white powder 

 or a translucent gum-like mass. It dissolves very slightly 

 in boiling water, yielding an opalescent solution. The 

 composition of this substance was found by Thomsen to 

 be CsHioOs. 



Xylin differs from pararabin and pectose in not being 

 soluble in milk of lime. It is converted by boiling with 

 dilute sulphuric acid into a crystallizable sxigar, xylose, 

 whose properties have been but little investigated. 



Flax-seed Mucilage, CbHioOs, resembles metarabiu, 

 but by action of hot dilute acids is resolved into cellulose 

 and a gum, which latter is further transformed into dex- 

 trose. The yield of cellulose is about four per cent. 



Quince-Seed Mucilage appears to be a compound of 

 cellulose and a body like arabin. On boiling with dilute 

 sulphuric acid it yields nearly one-third its weight of cel- 

 lulose, together with a soluble gum and a sugar, the last 

 being a result of the alteration of the gum. The sugar 

 is similar to arabinose. 



The Soluble Gums in Bread-grains.. — In the bread- 

 grains, freely soluble gums occur often in considerable 

 proportion. 



TABLE OF THE PKOPOETIOKS {per Cent.) OF GUM* IN VARIOUS AIK-DRY 

 GRAINS OR MILL PRODUCTS. 



(According to Von Bibra^ 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 



Eye 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 " gum " In the above table (which dates from 1859), Includes per- 

 haps solvible starch and dextrin In some, if not all cases, and, accord- 

 ing to O'SuUlvan, barley, wheat and rye contain two distinct left-pol- 

 arizing gums, Avhicli he terms a-amylan and b-amylan. These occur in 

 barley to the extent of. 2.3 per cent. By action of acids they yield 

 dextrose. 



