CHAPTER V 



CONDUCTING TISSUE 



All cells of which the primary or secondary function is that 

 of conduction are included under conducting tissue. It will 

 be understood how important the conducting tissue is when the 

 enormous quantity of water absorbed by a plant during a 

 growing season is considered. It will then be realized that 

 the conducting system must be highly developed in order to 

 transport this water from one organ to another, and, in fact, 

 to all the cells of the plant. Special attention must be given to 

 the occurrence, the structure, the direction of conduction, and 

 to the nature of the conducted material. 



The cells or ^cell groups comprising the conducting tissue 

 are vessels and tracheids, sieve tubes, medullary ray cells, latex 

 tubes, and parenchyma. 



VESSELS 



Vessels and tracheids form the principal upward con- 

 ducting tissue of plants. They receive the soil water expressed 

 from the cortical parenchyma cells located in the region of the 

 root, immediately back of the root hair zone. This soil water, 

 with dissolved crude inorganic and organic food materials, after 

 entering the vessels and tracheids passes up the stem. The 

 cells needing water at the different heights absorb it from the 

 vessels, the excess finally reaching the leaves. When the stem 

 branches, the water passes into the vessels of the branches and 

 finally to the leaves of the branch. In certain special cases the 

 vessels conduct upward soluble food material. In spring sugary 

 sap flows upward through the vessels of the sugar maple. 



Vessels are tubes, often of great length, formed from a number 

 of superimposed cells, in which the end walls have become 

 absorbed. The vessels therefore offer little resistance to the 

 transference of water from the roots to the leaves of a plant. 



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