FORM AND ARRANGEMENT OF CELLS. 3 



one direction, exhibit an hexagonal form (figs. 14, 15), and hence the 

 tissue is sometimes called heocagonienchyma (t^ofyuvios, six-angled); it is 



seen in the pith of the Elder, and in young palm stems. 2. Sphceren- 

 chyma (yQatget, a sphere), spheroidal cells (fig. 5). 3. Merenchyma 

 (fiYigva, to revolve), ellipsoidal cells (fig. 6). 4. Ovenchyma (&POI/, an egg), 

 oval cells. Round, elliptical, and oval cells, are common in herbaceous 

 plants. 5. Conenchyma (x.avo$, a cone), conical cells, as hairs. 6. Columnar 

 cellular tissue, divided into Cylindrenchyma (xt^/i/Sjo?, a cylinder), cylin- 

 drical cells, as in Chara (fig. 17 a), and Piismenchyma (naia^a,, a prism), 

 prismatical cells, seen in the bark of some plants (fig. 10). When 

 compressed, prismatical cells form the muriform (murus, a wall, like 

 bricks of a building) tissue of the medullary rays of woody stems, and 

 when much shortened they assume a tabular form, constituting Pinen- 

 chyma (vivu.%, a table), tabular cells (fig. 11), or square cells (fig. 9). 

 7. Prosenchyma (^[ 29), or Atractenchyma (oiT^atxros, a spindle), fusi- 

 form or spindle-shaped cells, seen in bark and wood (fig. 2). 8. 

 Colpenchyma (x.favo$, a sinus or fold), sinuous or waved cells, as in the 

 cuticle of leaves. 9. Cladenchyma (x^xlog, a branch), branched cells, 

 as in some hairs. 10. Actinenchyma (CCX.TH/, a ray), stellate or radiat- 

 ing cells, as in Juncus and Musa (fig. 16). 11. Dcedalenchyma (B/JXof, 

 entangled), entangled cells, as in some Fungi. 



15 



6. The size of cells varies not less than their figure in different 

 plants, and in different parts of the same plant. They are frequently 

 seen from 5 ^o to ^Jo of an inch in diameter. In cork, which is cellu- 

 lar, Hooke found more than a thousand in the length of an inch. 



7. Each cell consists originally of a separate membrane, but in the 

 progress of growth the walls of contiguous cells may become united. 

 When cells are united by their extremities (fig. 17), their partitions 



Figs. 9, 10, 11, 12, 13. Figures representing the forms of cells. Figs. 14, 15. Hexagonal cells. 

 Fig. 16. Brandling cells of Vicia Faba. 1 1, Intercellular lacuna;. 



