SPIRAL CELLS. 



369 



(Fig. 157). Such " spiral cells" are found most abundantly in 

 the leaves of certain Orchide- 

 0U8 plants, immediately be- 

 neath the cuticle, where they 

 are brought into view by ver- 



FlG. 157. 



Spiral cells of leaf of Oncidium. 



Spiral fibres of Seed-coat ofCoUffmia, 



tical sections, and they may be obtained in an isolated state, by 

 macerating the leaf and peeling off the cuticle, so as to expose 

 the layer beneath, which is then easily separated into its com- 

 ponents. In an Orchideous plant named Saccolabium guttatum, 

 the spiral cells are unusually long, and have spires winding in 

 opposite directions; so that, by their mutual intersection, a 

 series of diamond-shaped markings is produced. Spiral cells 

 are often found upon the surface of the testa or outer coat of 

 seeds ; and in the Collomia grandiflora, the Salvia verbenaca (wild 

 clary), and some other plants, the membrane of these cells is so 

 weak, and the elasticity of their fibres so great, that when the 

 membrane is softened by the action of water, the fibres suddenly 

 uncoil and elongate themselves (Fig. 158), springing out, as it 

 were, from the surface of the seed, to which they give a peculiar 

 flocculent appearance. This very curious phenomenon, which 

 greatly preplexes those who are ignorant of its real nature, may 

 be best observed in the following manner : — A very thin trans- 

 verse slice of the seed should first be cut, and laid upon the 

 lower glass of the aquatic box ; the cover should then be pressed 

 down, and the box placed upon the stage, so that the body of 

 the microscope may be exactly "focussed" to the object, the 

 power employed being the 1 inch, 2-3ds inch, or the J inch ob- 

 jective. The cover of the aquatic box being then removed, a 

 small drop of water should be placed on that part of its internal 

 surface, with which the slice of the seed had been in contact ; 

 and the cover being replaced, the object should be immediately 

 looked at. It is important that the slice of the seed should be 

 very thin, for two reasons ; first that the view of the spires may 

 not be confused by their aggregation in too great numbers ; and 

 second, that the drop of water should be held in its place bv 



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