BOTANY FOR BEGINNERS 



CHAP. 



(See that no sulphuric acid finds its way on to the 



a blue colour, 

 microscope). 



EXPT. 72. Take some cotton wool and first soak it in alcohol for 

 half an hour to drive out the air. Mount it in water. Examine it first 

 under a low power, then under a high power. Note-^ 



(i) The twisted filaments, which consist of single cells. 



(ii) The thick colourless cell-walls. 



(iii) The remains of the protoplasm seen clinging to the interior of 

 the cell-walls. 



(iv) Treat a small quantity with iodine solution the walls stain 

 slightly yellow. 



(v) Add a drop of strong sulphuric acid after the cover-glass has been 

 removed, when a distinct blue colour will be seen. 



Evidently cotton consists principally of cellulose. 



FIG. 103. Section of endosperm 

 of Date. (X 400.) 



FIG. 104. Cotton 

 fibres. ' 



FIG. 105. Longi- 

 tudinal section 

 of a Match, 

 showing pits. 



EXPT. 73. Cut sections from a cork and soak them in alcohol. 

 Mount the thinnest in water and examine with the microscope. 

 Observe : 



(i) The cell-walls, which have a clear outline. The cells have lost 

 their contents. 



(ii) Treat another section with iodine solution, the walls stain yellow. 



(iii) Treat another section with iodine and sulphuric acid, the walls 

 stain yellow or brown, not blue ; neither do they swell with sulphuric 

 acid, but keep their outline. 



EXPT. 74. Cut sections from a wooden match and soak them in 

 alcohol to remove the air bubbles. Mount a thin one in glycerine, and 

 observe the cell-walls, which are seen to have a number of pits (Fig. 105). 



(i) Treat a section with iodine ; it stains yellow. 



(ii) Treat another section with iodine and sulphuric acid ; it swells 

 and stains brown. 



NOTE. A cellulose wall can thus be distinguished from a lignified 

 or a corky wall because it gives a blue colour with iodine and sulphuric 



