94 PRACTICAL BOTANY 



Note on Mucilaginous Walls. 



Soak a few seeds of Linum (Linseed) in water for an hour or 

 so. Observe that the surface of the seed, which was originally 

 glossy and hard, is now covered by a pearly layer of transparent, 

 swollen mucilage, of considerable thickness. 



a. Cut thin transverse sections of a dry seed (the razor being 

 used dry, or moistened with alcohol, or with pure glycerine) : 

 mount in pure glycerine, and examine first under a low power. 

 Neglecting the internal structure, observe the superficial layer 

 of cells, of the testa, or outer coat. Note especially their thick, 

 stratified walls, of which a superficial layer (the cuticle) may be 

 recognized by its high refractive power, also the middle lamella, 

 easily recognized by its optical properties. 



Dilute the pure glycerine with water, and observe the thickened 

 walls : their substance will be seen to swell slowly, and the 

 stratified structure to become more apparent. The swelling will 

 often be seen to rupture the outer layer of cuticle, the swollen 

 mass protruding, and constituting the transparent layer seen on 

 soaking the whole seed. Thus the mucilaginous wall, though it 

 swells, is not dissolved. The middle lamella remains as a more 

 or less definite layer, which does not swell. 



b. Treat a similar section with potash, and observe the much 

 more quick and complete swelling of the mucilaginous walls. 

 The action is intensified by slightly warming the slide. 



c. Treat a section, which has been soaked in water for a few 

 minutes, with iodine solution. The swollen mucilage does not 

 stain to any appreciable extent. 



d. Treat a similar section with Hoffmann's blue. The swollen 

 mucilage does not stain appreciably. These preparations will 

 serve to bring out clearly the limits of the swollen mass, which 

 will appear as a transparent zone round the sections, sharply 

 defined from the surrounding coloured fluid. 



e. Treat a section with corallin-soda solution : the mucilaginous 

 walls stain pink. 



/. Apply the test of iodine and sulphuric acid : a more or less 

 distinct bluish tinge may be seen. This is absent from gums, 

 which are difficult to distinguish from mucilage by micro- 

 chemical tests. 



