11.] PLANT STRUCTURE AND GROWTH. 27 
The dast-tissue consists of very long, thin cells, 
drawn out like threads, and very 
tough. The wood-tissue is likewise 
composed of long cells, which fit e B 
into each other closely, but the 
cells are not nearly so long as 
those of the bast. The bast-tissue ma 
supplies the dast of the gardener, bo ecaspr = gg 
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 dast-tisswe 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 ce//ulose being deposited 
equally over the whole inner surface of the cell, cer- 
en 
Wy 
yy) 
i 
Y 
(Ci ]eceeaeeanaranes 
Fic. 30. Fic. 31. Fic. 32. Fic. 33 
tain portions are left unthickened, and the result is to 
make them appear dotted or pitted; these are known 
as dotted cells or vessels (fig. 30); in others it is de- 
