SECTION THREE 



Technique: 



1 . Heat the potassium hydroxide solution in an open beaker to 

 boiling point. 



2. Place the sections in the beaker which should now be covered 

 with a clock glass, and continue the boiling for half an hour. 



3. Remove the sections and wash in 90% alcohol. 



4. Treat the section with Gram's iodine solution. 



Results: 



Chitin, if present in the tissue, will be indicated by a reddish- 

 violet colour. 



Chlorides 



Occur in roots of Dauctis carota and Beta; Primula ohconica; 



solanum 



Solutions required: 



A. Silver nitrate 5% aqueous. 



B. Nitric acid 1-5% aqueous. 



Technique: 



1 . Sections, which must be cut with a scrupulously clean razor, 

 are placed in a drop of the silver nitrate solution on a slide. 



2. Examine, without a coverslip, under the microscope, when 

 the silver chloride precipitate will appear black. 



Note: The presence of chlorides in the tissue is indicated by 

 a precipitate which is white to the naked eye. 



3. By means of glass needles transfer the sections to a drop of 

 the diluted nitric acid solution on another sHde. 



4. Examine under the microscope when it will be observed that 

 the acid clears the sections sufficiently to allow localization of the 

 reaction. 



5. Repeat stage 3 (above); add a few drops of ammonia solu- 

 tion to the slide until the precipitate just dissolves. 



237 



