CHAPTER X 

 CONDUCTING TISSUES 



The crude materials in solution absorbed by the 

 root hairs must be transported to the leaves for manu- 

 facture into nutrients. The nutrients produced by 

 the leaves must subsequently be distributed to all 

 parts of the plant. In view of these facts the necessity 

 of a system for the conduction or transportation of 

 crude and manufactured materials is clearly apparent. 

 The absorbing tissues are located at the two extremes 

 of the plant, the root hairs at the lower, the leaves 

 at the upper; and communication between these is 

 effected by a system of tubular structures. The 

 conducting tissues are found in all parts of the plant, 

 with the exception of the outer bark, the epidermal 

 membranes and the seed. The outer layers of the 

 bark consist of dead cells; and those cells near the 

 phellogen are nourished by transfusion of nutrients 

 from cell to cell. The epidermal and seed tissues 

 are nourished in the same manner as the cells of the 

 inner bark. The structures concerned in the trans- 

 portation of materials in the plant include ducts, 

 sieve tubes, medullary rays, latex tubes and per- 

 forated parenchyma. 



Ducts. — Ducts, tracheae or vessels are continuous 



tubes extending for considerable distances within the 



plant body. They are formed by fusion of a vertical 



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