CHAPTER XV 

 THE MOVEMENT OF WATER THROUGH THE PLANT 



Most terrestrial plants obtain the water which is necessary for their 

 existence from the soil. An overwhelmingly large proportion of the water 

 which is absorbed by the roots of land plants is lost in the process of trans- 

 piration. Smaller quantities are utilized in growth and in photosynthesis, 

 and in some species limited amounts of water may be lost by guttation. 

 Water must therefore move through the intervening tissues and organs from 

 the absorbing regions of the root to the tissues in which it is utilized, or 

 from which it passes out of the plant. The process whereby water moves 

 through the plant is often termed the conduction^ transport, or translocation 

 of water. 



In herbaceous species and many shrubby plants the distance through 

 which water moves in passing from the root tips to the leaves is usually 

 not more than a few feet. Even in such plants appearances are sometimes 

 deceptive, as some herbaceous and shrubby species such as alfalfa may have 

 such deep root systems that some of the absorbed water often ascends for 

 distances as great as twenty or more feet before it reaches the level of the soil 

 surface. It is in trees, however, in which the most striking illustrations of 

 the upward movement of water occur. The tallest tree of Avhich we have 

 an authentic record is a specimen of the Coast Redwood {Sequoia semper- 

 virens) which has attained a height of 364 feet (Tiemann, 1935)- Many 

 other individuals of this species and of several others, including the Big Trees 

 {Sequoia gigantea) of California, the Douglas Firs {Pseudotsuga mucronata) 

 of the Pacific Northwest, and the Blue Gums {Eucalyptus) of Australia 

 exceed 300 feet in height. Trees ranging from 100 to 200 feet in height were 

 of common occurrence in the virgin forests of eastern North America. Since 

 the root systems of trees always penetrate at least a few feet into the ground, 

 the actual vertical distance through which at least a part of the water absorbed 

 is elevated is always more than the height of the tree. In trees, therefore, 

 water must ascend to heights ranging up to nearly 400 feet above the level of 

 water absorption. 



The mechanism by which this feat is accomplished in tall trees has been 



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