VEGETATIVE ORGANS OF PLANTS. 255 



and position, and are sometimes dotted and perforated, 

 as will be explained hereafter 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. 



