TISSUES. 5 



16. In the organs of generation in certain plants, 

 fibre is seen assuming very peculiar dispositions and 

 arrangements, which, according to some, constitute a 

 variety of fibrous cellular tissue. 



1 7 . Fibrous tissue constitutes a great portion of the 

 woody matter of all plants as well as the bark, and is 

 the formative material in all hempen goods. 



Vascular Tissue. 



The best 



18. Vascular tissue consists of two forms, spiral ves- 

 sels and ducts, though transitional states of one form 

 into the other undoubtedly can be seen. 



19. Spiral vessels are simple or compound. 

 definition of this structure is a modifica- 

 tion of Links spiral vessels are more or 

 less regular cylindrical tubes formed by 

 spirally wound fibre within a tender mem- 

 brane. 



20. Simple spiral vessels are those in 

 which one fibre alone is twisted within the 

 membrane ; compound ones in which there 

 are two or more. 



21. The fibre of a spiral vessel is most 

 probably solid, and the termination of the 

 vessel conical or accuminate. 



22. Spiral vessels exist chiefly as a layer of tissue 

 (called the medullary sheath) immediately surrounding 

 the pith ; they are found in the roots of a few exoge- 

 nous as well as endogenous plants, and although 

 more immediately proper to the true flowering plants, 

 have likewise been found in Ferns and the capsules of 

 young mosses ; and, it must be remembered, are few 

 and small in the tribe of the pines or Coniferse. 



23. Ducts are of two kinds, ducts and proper 

 ducts. 



B 3 



I 



