CHAPTER VII 



THE COVERING TISSUES 



Coveeing, or protective tissues, are found on all 

 exposed surfaces of the plant. The general function 

 of these tissues is the protection of the vital parts of 

 the plant from injury due to climatic variation or 

 other agents beyond the control of the plant. In 

 northern or even temperate latitudes the plant is 

 subjected to great and fairly rapid fluctuations in 

 temperature, which, if not guarded against, would 

 cause injury to the more delicate plant organs. The 

 covering tissues act as insulators and prevent temper- 

 ature variations from injuring the plant. In certain 

 instances the plant possesses the faculty of adjusting 

 itself to long-continued periods of high or low temper- 

 ature; but this adjustment entails a modification 

 of the covering tissues. Plants in tropical regions 

 require protection against the excessive heat of the 

 sun during the dry season and an undue access of water 

 during the rainy period. Both of these adverse con- 

 ditions are met by modifications in the structure of 

 the covering tissues. The covering tissues of certain 

 floral organs secrete substances which influence pollin- 

 ation. By reason of differences in location, formation, 

 structure and chemical composition, the covering 

 tissues of the plant are subdivided into ; (a) epidermal 

 tissues, including plant hairs, and (6) periderm. 



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