THE GYMNOSPERMAE : CONIFERALES AND TAXALES 66i 



The main stem is cylindrical and is covered with a very rugged, scaly 

 bark. The stem branches monopodially, forming lateral branches in whorls 

 from buds developed in the axils of scale leaves at the end of each year's 

 growth. This regular development of branches gives the young tree a very 

 symmetrical appearance, but in old specimens the symmetry is lost by the 

 death of the lower branches, and the irregular growth of the remainder. 

 The tree then assumes the familiar umbrella form. The scars marking the 

 position of the lost whorls of branches can be seen on the main trunk of the 

 old tree and give a useful indication of its age. 



Leaf pair 



Foliar spur 



: Long shoot 



Fig. 660. — Pitiiis sylrestris. 

 Young branch showing foliar 

 spurs bearing paired leaves. 



In monopodial branching the main stem continues indefinitely in active 

 growth as the leading shoot. If this is accidentally destroyed there is a most 

 interesting " struggle for precedence " which Errera has described. Two or 

 more of the uppermost lateral branches assume the vertical position and a 

 competition for leadership ensues. When the strongest of these shoots has 

 asserted its dominance it replaces the missing leader and the others fall 

 back into the lateral position again. 



In addition to the branches which have unlimited apical growth there 

 are very numerous " dwarf shoots " or foliar spurs of limited growth, which 

 arise in the axils of scale leaves borne on the main branches (Fig. 660). The 

 leaves are of two kinds. Firstly there are the foliage leaves or " needles " 

 which appear only on the foliar spurs. The number of such leaves produced 

 on a spur may be one, two, three or five according to the species, but in 

 Pinus sylvestris there are only two. The leaves have a smooth surface and 



