63 



HOW CROPS GROW. 



corn and barley husks, contain 6 to 20 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 ti'anslucent 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 CeHioOs. 



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 sugar;- xylose, 

 whose properties have bsen but little investigated. 



Flax-seed Mucilage, CellioOs, resembles metarabin, 

 but by action of hot dilute acids is resolved into cellulose 

 and a gum, which latter is further transformed intadex- 

 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 PKOPORTIONS (per Cent.) OF GTJM* IS VABIOUS AIE-DBY 

 GRAINS OK MILL PEOD0CTS. 



(According to Von Bibra, Die Oetreidearten mid das Brod.) 



AVheat kernel 4.50 



"WTieat floiir, superfine 6.25 



Spelt flour ( Triticum spelta) .. 2.48 



wheat bran 8.86 



Spelt bran.' 12.52 



Rye kernel 4.10 



Eye flour 7.25 



Eye bran 10.40 



Barley flour 6.33 



Barley bran 6.88 



Oat meal 3. so 



Rice flour 2.00 



Millet flour 10.6O 



Maize meal 3.05 



Buckwheat flour 2.85 



* The " gum " in the above table (which dates from 1859), includes per- 

 haps soluble starch and dextrin in some, if not all case.s, and, accord- 

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

 arizing gums, which he terras a-amylan and b-arn,ylan. These occur in 

 I^.^^lcy to the extent of 2.3 per cent. By action of acids tliev yield 

 dextrose. 



