62 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 maybe 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 C 6 H 10 6 . 



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 been but little investigated. 



Flax-seed Mucilage, C 6 H 10 5 , resembles metarabin, 

 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 PROPORTIONS (jtfrcfnt.) OF CJUM* IX VAKIOfS AIR-DRY 

 GRAINS OK MILL PKOIUTTS. 



(According to Von ISihr", l>i< Ciiriidinrti-n mul <l* Hrofl.) 



Wheat kernel 4.50 Barley flour 6.33 



Wheat Hour, superfine 6.'-'."> Barley bran c.vs 



Spelt Hi >ur i Tfitii-niii s/,i-/hi,.. L'.4s Oat ii'it-al :?.r>0 



Wheat ]>ran 8.85 Rice Hour L'.IMI 



Spdt bran 12..^' Millet flour Hu;o 



Rye kernel 4.10 Mai/e meal 3.05 



Ryefionr ~.-s> Buckwheat flour 2.85 



live bran 10.40 



* The "fjuni " in the above table ('which dates from 1.")9>, includes per- 

 haps soluble starch and dextrin in some, i! not all cases, and. accord- 

 ing to ( >'Su!livan. barley, wheat and rye contain two distinct left-pol- 

 anzlng giuns, which be terms a-amylan ami ii-imti/hni. These occur iit 

 barley to the extent of 2.3 per cent. 15y action' of acids they yield 

 dextrose. 



