36 PRACTICAL BOTANY. 



i. Coloured red by tincture of alkanet. 



ii. Coloured blue by Hanstein's aniline violet 



iii. Decomposed by potash. 



iv. Soluble in alcohol and ether. 



7c. Caoutchouc : occurs in the laticiferous vessels in 

 the form of granules of different size in different plants : 

 stains red with alkannin solution. By means of this 

 reaction good preparations of laticiferous vessels can 

 be made. 



I. The Cell-sap may contain in solution : 



1. Colouring matters. 



2. Cane-sugar (as in the Beet-root) (C 12 H 22 O n ), 

 which does not give a reaction with Fehling's solution. 

 See p. 20. If much is present it may be made to 

 crystallise out by treatment with absolute alcohol. 



3. Grape-sugar (Glucose) (C 6 H 12 O 6 ). 



If a section be boiled in dilute Fehling's solution, 

 it will, if the cells contain glucose, turn yellow, owing 

 to the reduction of the copper. See p. 20. 



The precipitate (cuprous oxide) appears in the cells 

 under the microscope as small black granules. 



4. Inulin (C 6 H 10 O 5 ). 



When the material or the section has been treated 

 with alcohol, the inulin is precipitated in the form of 

 sphsero-crystals, which may be readily observed. These 

 crystals are insoluble in cold, but readily soluble in 

 warm water, and in dilute acids and alkalies. 



Coloured slightly brown by iodine. 



5. Asparagin (C 4 H 8 N 2 O 3 ). 



When a section of a tissue containing asparagin is 

 treated with absolute alcohol for some time, the aspara- 

 gin is precipitated in the form of prismatic crystals, 



