VEGETATIVE ORGANS OF PLANTS. 255 



and position, and are sometimes dotted and perforated, 

 as will be explained hertJafter— Fig. 53, p. 301. 



Bast-Tissue is made up of long and slender cells, 

 similar to those of wood-tissue, but commonly more del- 

 icate and flexible. The name is derived from the occur- 

 rence of this tissue in the bast, or inner bark. Linen, 

 hemp, and most textile materials of vegetable origin, 

 cotton excepted, consist of bast-fibers. Bast-cells occupy 

 a place in rind, corresponding to that held by wood- 

 cells in the interior of the stem — Fig.' 49, p. 293. 



Vascular Tissue is the term applied to those un- 

 branched Tubes and Ducts which are found in all the 

 higher orders of plants, interpenetrating the cellular 

 tissue. There are several varieties of ducts, viz. , dotted 

 ducts, ringed or annular ducts, and spiral ducts, of 

 which illustrations will be given when the minute struc- 

 ture of the stem comes under notice — Fig. 49, p. 293. 



The formation of vascular tissue takes place by a sim- 

 ple alteration in cellular tissue. A longitudinal series of 

 adhering cells represents a tube, save that the bore is 

 obstructed with numerous transverse partitions. By the 

 removal or perforation of these partitions a tube is devel- 

 oped. This removal or perforation actually takes place 

 in the living plant by a process of absorption. 



