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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