INULIN. 



51 



form which are distinct!}* radiating in structure. Occasionally 

 these masses have large rifts which run across the surface of the 

 sphere. 



In composition, inulin closely resembles starch, but does not 

 give any color with iodine. To de- 

 tect it when in solution, a thin sec- 

 tion of the plant containing it is 

 moistened on the glass slide with 

 absolute alcohol, when a cloudy pre- 

 cipitate will at once appear ; in a 

 short time (the supply of alcohol 

 having been replenished as it evap- 

 orates) the specimen grows clearer, 

 and small sphserocrystals of inulin 

 are seen. If now the specimen is 

 carefully washed with water, the 

 smaller granules disappear and the 

 well-defined remain. 



184. The carbohydrates dissolyed 

 in the cell-sap may be grouped in two 

 classes : (1) those which are isomers 

 of cellulose (i. e., have the same per- 

 centage composition, C 6 H 10 O 5 ) , and (2) the sugars. 



1. The isomers of cellulose are mucilage, gums, and dextrin, 

 all of which are probably derivatives of starch. Various sub- 

 stances intermediate between them have been described, but the 

 above are all that need now be taken into account, (a) Mucilage, 

 when not plainly resulting from the breaking up of the cell- 

 wall, is colored red by rosolic acid, and the color is not readily 

 removed by alcohol, (b) Tlie gums, of which cherry gum 

 may be taken as an example, are not tinged by rosolic acid, 

 (c) Dextrin can be detected by Trommer's test, which Sachs ap- 

 plies as follows : a section which is at least a few cells in thick- 

 ness is placed in a porcelain capsule with a strong solution of 

 cupric sulphate, and the liquid is heated to boiling ; the specimen 

 is then washed in water, and dipped at once in hot potassa. 

 If the cells contain either dextrin or grape-sugar, there will 

 immediately appear a reddish precipitate. To discriminate be- 

 tween dextrin and grape-sugar, it is merely necessary to keep 

 portions of the plant to be examined in 90 or 95 per cent alcohol, 

 which will dissolve out the sugar and leave the dextrin, if any 



FIG. 35. Spliaerocrystala of inulin from root of Cicbory treated with alcohol f. 

 (Jacobs. ) . 



