THE SEED PLANTS 



289 



tissue in the ferns, but in the pines and their relatives the 



vascular tissue is organized into a stem that may attain great 



height and thickness (fig. 222). These plants have been 



highly successful in the struggle for 



light. Such plants also have quite 



extensive woody root systems, which 



serve to anchor these great trees and 



to gather the water and substances 



in solution that are conducted through 



the whole length of the stem to the 



leaves. 



The significance of the stems of 

 gymnosperms and some angiosperms 

 to those industries that use timber 

 is difficult to estimate. Timber is 

 used for all sorts of useful and orna- 

 mental products, and many kinds of 

 industry are dependent upon timber ; 

 but it must be remembered that 

 woody stems are developed as struc- 

 tures which support leaves and con- 

 duct food materials to and from them, 

 in connection with the plants' strug- 

 gle to live, and that man's use of 

 this timber is, botanically, merely 

 incidental. 



274. Pine cones. Two kinds of 

 cones are borne upon pines : one is 

 the seed-forming cone (fig. 223) ; the 

 other is the staminate cone. The 

 seed cone is composed of heavy, leaf- 

 like parts, on the upper sides of 

 which the developing seeds or ovules 

 are formed. Within the ovule the egg is produced (fig. 224). 

 The staminate cones appear early in the spring, shed their 

 pollen, and soon wither and fall to the ground. These cones 



FIG. 224. Diagram of part of 



a seed cone of a pine, with 



ovules in normal position 



S, aporophylls, or leaf-like parts 

 of the cone; O, ovule; /, the 

 covering of the ovule, called 

 the integument ; f'G, the female 

 gametophyte, which bears the 

 archegonium A, in which the 

 egg is formed ; Pt, pollen tubes 

 from pollen grains which lie 

 upon the tip of the ovule 



