CKIBROSE-CELLS. 



91 



ITT Cribrose-cells. Sieve-cells, or Sieve-tubes. 



279. In the inner bark of stems of dicotyledons with normal 

 structure certain long cells of peculiar character are found as- 

 sociated with bast-fibres. They 

 are of tubular or prismatic form, 

 and are characterized by the pres- 

 ence of circumscribed panels in 

 the walls, in which are numerous 

 fine perforations permitting com- 

 munication between contiguous 

 cells. The panels are known as 

 sieve-plates ; the perforations, as 

 sieve-pores. These cells consti- 

 tute an essential, though by no 



means always a conspicuous, element of fibro-vascular bundles. 



Taken collectively, 

 "I they may be known 

 as cribriform tissue. 

 By their union end to 

 rnd they appear like 

 long tubes with the 

 continuity interrupted 

 here and there by cross 

 partitions. These par- 

 titions which separate 

 the individual cells 

 are sometimes nearly 

 horizontal, but more 

 generally oblique, as 

 shown in the annexed 

 figures where they 

 mostly cut the lateral 

 wall of the cell at a 

 sharp angle. 



280. The walls of 

 cribrose-cells are 

 never lignified ; on 

 the contrary, they are 



FIG. 69. PInus sylvestris. Face view of radial wall containing two cribrose-plates 

 wholly deprived of callus. **?*. (Janczewski.) 



FIG. 70. Finns sylvestris. Radial wall of a young tube, face view. The future cri- 

 brose-plates are composed of callus-cylinders, filling tlie meshes of a cellulose network. 

 ll f*. (Janczewski.) 



FIG 71 Cribrose-cells in Vitis vinifera ; A, transverse anastomosis of two cribrose- 



