CHAPTER VIII 

 SUPPORTING TISSUES 



THE necessity for a framework or skeleton arises 

 fairly early in the life of the plant, and the supporting 

 or mechanical tissues which serve this purpose are 

 developed from groups of cells in the plerom zone. 

 The process of formation involves the deposition of 

 lignin around the original cellulose walls of certain 

 plerom cells. Lignification of the cell walls may be 

 accompanied by a great increase in the length of the 

 plerom cells so changed. The mechanical tissues not 

 only serve as a framework, but are also protective 

 tissues, in that they enable the plant to resist the 

 effects of wind, the attacks of animals and other 

 external forces which might injure or uproot it. In 

 large trees supporting cells form the bulk of the tissues 

 present, because it is necessary that a weight of per- 

 haps several hundred pounds be sustained in the posi- 

 tion most favorable for growth. 



The supporting elements of the plant include 

 fibrous tissues, schlerenchymatic or stone cell tissue 

 and collenchymatic tissue. While fibrous tissues and 

 collenchyma may be formed early in plant life, stone 

 cell tissue represents a later development. The 

 endodermal cells which form the inner boundary of 

 the periblem region possess thickened walls and may 

 function as a supporting tissue in the early stages of 

 growth. 



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