THE PINE 121 



lower surfaces are air-pores, like those on the lower surface of the 

 fern leaf. In a cross section through a pine leaf (Fig. 69) we find a 

 variety of tissues, in general much like those of the stem. In the 

 central part of the section are two vascular bundles, 1 each composed 

 of wood and bast ; the wood is that part of each bundle turned toward 

 the upper side, and the bast is the part toward the lower side of the 

 leaf. 



146. Roots. The long tap root of the pine is continuous 

 with the trunk ; it may grow downward for a great distance. 

 The tap root gives off branch roots, which in turn branch, 

 and both the tap root and the branch roots form bark and 

 grow in thickness in much the same way as the trunk does. 

 There is a marked difference between the way in which 

 branches start from the stem and that in which branch 

 roots start from the tap root. A branch of the stem begins 

 as a surface swelling at the growing point of the stem ; a 

 branch root begins its development within the tap root, 

 some distance back of the growing point and just outside the 

 ring of vascular bundles ; so the new root must break its way 

 through the outer tissues of the older root within which it 

 has begun to grow. Although we ordinarily see little of the 

 roots of the pine, we must remember that they really make 

 up a large system, comparable in size with the trunk and its 

 branches. The weight of the parts of a tree above ground, 

 and the great pressure exerted upon it by the winds, make 

 necessary an extensive root system that will anchor the tree 

 firmly in the soil. 



A root of the pine, as of the fern, bears root hairs just back 

 of the growing point. New root hairs are constantly being 

 formed in this region, but they soon die and fall or are rubbed 

 off. For this reason the zone in which root hairs are borne is a 

 short one. Since it is only through the root hairs that water 

 and other substances are taken from the soil, this work of 

 absorption can go on in only a small part of the root system of 



1 In some species, including the white pine, the leaf contains only one vascular 

 bundle. 



