MICROSCOPIC STRUCTURE OF PHANEROGAMIC PLANTS. 361 



plants, immediately beneath the cuticle, where they are brought into 

 view by vertical 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 components. In an Or- 

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

 seeds: arid in the Coltomia grandifiora, the Salvia verbeuaca (Wild Clary), 

 and some other plants, the membrane of these cells if 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. 245), springing out, as it were, from the surface of the seed, to 

 liyhich they give a peculiar flocculent appearance. This very curious phe- 



Fia. 245. 



Fia. 244. 



-* 



Spiral cells of leaf of Oncidium. Spiral fibres of Seed-coat of Collomia, 



nomenon, which is not unfrequently spoken of by persons ignorant of its 

 true nature as the ' germination' of the seed, may be best observed in the 

 following manner: A very thin transverse 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 Microscope may be exactly focussed to the object, the power em- 

 ployed being the 1-inch, 2-3ds-inch, or the -inch. 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 im- 

 mediately 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 by capillary attraction, instead 

 of running down and leaving the object, as it will do if the glasses be too 

 widely separated. 



358. In some part or other 01 most Plants, we meet with cells con- 

 taining granules of starch, which especially abounds in the tubers of the 

 Potato, and in the seeds of Cereals and Legumes. Starch grains are ori- 

 ginally formed in the interior of Chlorophyll-corpuscles; but as they in- 



