CHAPTER XI 



STEM STRUCTURE 



Vocabulary 



Lenticels, openings in the bark for passage of air and water vapor. 



Radiating, extending out from the center. 



Fabric, woven material such as cloth. 



Perennial, living year after year. 



Dicotyledonous, plants having two cotyledons. (Dicots.) 



Monocotyledonous, plants having one cotyledon. (Monocots.) 



EXTERNAL STRUCTURE 



The external structure of all ordinary stems, though varying 

 greatly, has some points in common. It will be seen that there is 

 an outer covering, the epidermis or bark, which protects from 

 injury by storm and insects and prevents undue loss of water, as 

 a result of drought or cold. 



Lenticels. Through this bark are openings (lenticels) which 

 permit a regulated escape of water- vapor, and also admit air. 



Leaf Scars. On the bark will be found scars left by leaves of 

 preceding seasons, varying in location according as the leaves 

 were opposite or alternate, and having above them the buds for 

 the coming year's branches. On these scars will be found dots 

 marking the severed ends of the ducts, which can be traced into 

 the stem and found to extend to the roots. Over these scars is a 

 water-proof coat (abscission layer) which formed before the leaf 

 fell to protect the plant against the loss of so many leaves and 

 consequent bleeding from thousands of tiny wounds. 



Flower-bud and Fruit Scars. It frequently happens that the 

 bearing of a flower or fruit makes a scar differing from those made 



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