I,.] 



PLANT STRUCTURE AND GROWTH. 



27 





FIG. 29. 



W. wood-tissue. 

 B. bast-tissue. 



The bast-tisstie consists of very long, thin cells, 

 drawn out like threads, and very 

 tough. The 'wood-tissue is likewise 

 composed of long cells, which fit 

 into each other closely, but the 

 cells are not nearly so long as 

 those of the bast. The bast-tissue 

 supplies the bast of the gardener, 

 hemp, flax, and Russia-matting. 



The cambium zone is a narrow band of small, thin- 

 walled cells, which retain their power of growth and 

 division. It lies between the bast and the wood, and 

 is continually producing bast-tissue on the outer side, 

 and wood-tissue on the inner. 



Some cells which are united by their ends absorb 

 the cell-walls which separate them from the cell 

 immediately above or below them, and thus form a 

 long, open tube. Cells which have been thus modi- 

 fied are called ducts and vessels. 



In these a process of thickening the cell-wall goes 

 on, but instead of the new cellulose being deposited 

 equally over the whole inner surface of the cell, cer- 



<a 



FIG. 30. FIG. 31. FIG. 32. FIG. 33. 



tain portions are left unthickened, and the result is to 

 make them appear dotted or pitied; these are known 

 as dotted cells or vessels (fig. 30) ; in others it is de- 



