PRACTICAL WORK 137 



stain and leave it there for one minute. Take it out and wash 

 by gently moving the coverslip in water. Dry both sides of 

 the coverslip with blotting paper. Find out on which side the 

 smear is, and place the coverslip, smear downwards, on a small 

 drop of dilute glycerine on a slide. Examine with the high 

 power. 



B. THICK CELLULOSE AND MUCILAGINOUS CELL WALLS. 



(1) Examine in water sections of the date-stone (seed of the 

 date-palm) cut so as to show the elongated cells in transverse 

 section. Note the very thick cell walls. These are penetrated 

 by pits running from each cell cavity and ending at the middle 

 lamella of the cell wall (the middle lamella was the original 

 thin wall separating two adjacent cells before thickening took 

 place). The pits of adjacent cells are always exactly opposite 

 one another. 



Mount the section in a drop of Schulze's solution, and leave 

 for ten minutes. Then note that the mass of the cell wall is 

 stained purple (cellulose), while the middle lamella remains 

 unstained or only faintly stained. The mass of cellulose is 

 converted into sugar when the seed germinates and the sugar is 

 used for the respiration and growth of the young plant. 



(2) Examine a dry seed of the flax plant (linseed). Note 

 the sharp outline of the opaque seed. Now put the seed in a 

 watchglass with a little water. The outline of the seed is soon 

 surrounded by a transparent fringe. Compare the feel of the 

 dry and the wet seed between the fingers. 



Now examine a thin section of the seed dry under a coverslip, 

 and, running in a drop of water, watch the swelling of the surface 

 layer of cells. The middle lamellae of the walls separating the 

 cells can be distinguished from the swollen mucilaginous mass 

 of the walls. Note also the cuticle bounding the walls on the 

 outside. Methylene blue will stain the mucilage and render it 

 more easily visible. 



