STEM. 19 



leaf-buds in their axils, and producing flowers 

 and fruit. 



The points where leaves are borne are called 

 Nodi, knots ; the spaces between the leaves are 

 Liternodia, Internodes. 



The more erect a stem grows, the more 

 vigorous it is; and the more it deviates from 

 this direction to a horizontal or pendulous posi- 

 tion, the less is it vigorous. 



Some stems are developed under ground, 

 such as the Tubers of the Potato and the Cor- 

 mus of the Crocus, but they are known from 

 roots by the presence of leaves, and regular 

 leaf-buds upon their surface, as the shoots from 

 the eye of the potato. 



Stems increase in diameter in two ways. 



Either by the addition of new matter to the 

 outside of the wood and the inside of the bark ; 

 when they are Exogenous ; ex. Oak. 



Or by the addition of new matter to their in- 

 side; when they are Endogenous ; ex. Cane. 

 Palm. 



In Exogenous stems, the central portion, 

 which is harder and darker than that at the cir- 

 cumference, is called Heart-wood; while the 

 exterior, which is softer and lighter, is called 

 Alhurnum or Sap-wood. 



