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A^STATOMY AND PHYSIOLOGY OF 



in the internal Mib&tance of organs, for instance in pith, in bark, 

 &c., for here every cell is surrounded on all sides by other cells, 

 and exhibits as many flattened surfaces as there are cells standing 

 in connexion with it. Kie&er (^^Grundz, cler AQiatorroic der Pjimi- 

 zen/' § 127) sought to demonstrate, that the form of the cell must 

 necessarily be that of a rhombic dodccaheclrou under such circum- 

 stances, since this form encloses the greatest space within the 

 smallest amount of limits, and that their form is usually that of a 

 ihombric dodecahedron elongated in a perpendicular direction, be- 

 cause the primary form of the vegetable cell is not the sphere but 

 the ellipsoid. This proposition may be admitted theoretically, but 

 it would be a vain labour to seek actually to observe the form of 

 the rhombic dodecahedron in a cell in nature, since the contigu- 

 ous cells are ahvays far too unequal in size for them to become 



Fifj, 5 



Fig 6 



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5 



J A J 







Epilcnins of tlio lowei face of the leaf of 



lleUohoni&J-a^iidus 



PAroncliYinxtous cell«t from tho bark of 

 Jbtijjhoi but caiim Mibih. 



moulded into regular mathematical forms by their reciprocal pres- 

 sure. So that in cross sections of a parenchymatous tissue the cells 



very 



able number of sides (usually from iive to eight). It is therefore 

 more suitable to call such cells polyhedral instead of dodecahedral 

 On the more or less crowded ariangement of the cells it depends 

 whether the plane surfaces of these meet at acute angles (fig. 7) ; 

 or whethei*, when the cells are more loosely aggregated, the sur- 

 faces of contact are but small (fig. 6), and large portions of the 

 cell-walls between them remain unconnected with the neighbour- 

 ing cells. In the latter case, the free portions of the cells retain 

 their natural rounded form. In particular eases, however, the 

 portion of the cell-wall immediately surrounding a plane surface 

 in contact with another cell, glows out in a tubular form, so that 



