662 



A TEXTBOOK OF THEORETICAL BOTANY 



deeply sunken stomata, which are characteristic of xeromorphic types. The 

 second kind of leaf, termed the scale leaf, is developed as a protective 

 structure. These leaves are borne both on the main branches and also on 

 the foliar spurs and fall off as the branches mature. They are brown in 

 colour and are not capable of assimilation. Their function appears to be 

 to assist in the conservation of moisture around the branches. 



The Pine is an evergreen, that is to say, it does not shed all its leaves at 

 the same time. The foliage leaves persist for a number of years and only 

 fall when the spur is shed as a whole. 



Trees with no lower branches and with trunks without " knots " are of 

 special value for timber, and it is for this reason that it is customary to plant 

 Pines very close together so that the tendency to produce lateral branches is 

 repressed. Pine wood forms the " Deal " of commerce and is used in very 

 great quantities both in building construction and in making cheap furniture. 

 It is also employed almost exclusively for pit props in coal mines and as wood 

 pulp in paper manufacture. 



Anatomy of the Stem 



The anatomy of the stem resembles that of a dicotyledonous Angiosperm, 

 though on the whole it is simpler. The growing point is an obtuse cone of 



i i 



Scale leaves . 



Illy * x^'fi^y •^: ^ A'^ 









Stem initial 



Leaf initial 



Fig. 66 1. — Pinus sylvestris. Longitudinal section 

 through the growing point of a long shoot. 



