152 PHYSIOLOGICAL BOTANY. 



an inch in diameter. From this cells occur whose 

 diameters range all the way down to -^oW of an inch 

 in diameter. In the more solid tissues they range 

 from J to fa of an inch in length, and from T? V<7 to 

 -j-oVo in their cross-sections. Cells of the long staple 

 cotton wool are from one to two inches in length. 



386. Spiral and annular cells are formed when 

 rings, bands, or hoop-like processes 

 appear on the inner surfaces of the 

 walls ; in the spiral cell an uninter- 

 rupted fibrous process extends the 

 whole length of the cell in a spiral 

 coil (Fig. 483). The annular cell heis #3, spiral ceii from or- 



chid. 484, Annular cell from 



bands or hoop-like markings as though Mistletoe - 



the spiral fiber had been interrupted at several points 



(Fig. 484). 



387. Dotted or pitted cells are pro- 

 duced when the coatings on the inner sur- 

 face of the cell wall are not uniform in 

 thickness, leaving thin spots, or pits, which 

 485, Dotted or are m ore nearly transparent when viewed 



pitted cells from 



Eider pith. under the glass, than the more thickened 



parts of the wall ; hence the name (Fig. 485). 



388. Reticulated cells are produced by 

 coatings which are deposited or formed 

 upon the inner surface of the cell-wall, 

 where they at first appear in spots and 

 lines, of different sizes and lengths (Fig. 486, 



cell from the Mis- 



486). As the cell grows older, the markings tietoe. 

 increase in length, and touching each other, form an 

 irregular net-work. 



389. Collenchyma cells are cubical, cylindrical, or 

 irregular in form, whose walls are much thickened 



