THE CELL AS A MEMBER OF A GROUP. 35 



4. Vessels are made by the union of several cells, the 

 partition-walls disappearing while the union continues 

 at the margin. Such vessels may be dotted, reticula- 

 ted, annular, or spiral, from the deposit on the cell- 

 wall. Chap. V, Sec. 7. (See Fig. 11.) 



Bast-tubes, or bast- 

 fibers, are long, point- 

 ed, thick-walled tubes, 

 commonly united into 

 bundles. In. hemp, 

 flax, etc., they form 

 textile fibers, and they 

 are sometimes united 

 in the inner layer of 

 bark so as to form a 

 kind of lace, as in the 

 lace-bark of the West Fig. n. 



Indies. Sieve-tubes, or bast^vessels, result from the 

 joining of cells standing one above the other, the 

 partition-walls of which have become perforated. 

 Some have sieve-like perforations through their side 

 walls. 



Other vessels are simple or branched tubes, often 

 making a net-work, and containing a sort of milky 

 fluid called latex. This latter contains different sub- 

 stances in different plants, as gum, resin, opium, in- 

 dia-rubber, etc. 



5. In addition to the groups of cells which form 







