292 



INTRODUCTION TO BOTANY 



277. Seed formation. The oospore that is formed by the 

 union of the sperm and the egg grows and becomes the em- 

 bryo of a new pine plant. The tissues that surround this 

 developing embryo are partly absorbed by it and used in 

 nourishing it. By the time the embryo has developed root tip, 

 stem tip, and young leaves, the walls of the ovule have begun 

 to harden, and the whole structure is recognized as the seed 

 (fig. 226). When the pine cone opens, usually two years or 

 more from the time when pollination occurred, the seeds fall 

 to the ground and, if conditions are favorable, begin to ger- 

 minate. In germination the embryo 

 swells and bursts the seed coat, the 

 root grows downward into the soil, 

 and the leaves rise into the air ; in 

 time the embryo becomes a new tree, 

 which may bear cones and repeat 

 the process of reproduction. 



The cones may not shed their 

 seeds for several years (as in the 

 case of the lodgepole pine of the 

 Rocky Mountains), or not even 

 until the death of the tree, and the 

 young plants within the seeds may still remain alive and ready 

 to grow when properly placed for germination. It is becom- 

 ing a common practice of forestry to collect pine seeds in great 

 quantities and sow them over thousands of acres, thus resetting 

 or extending the areas in which pine seedlings grow. 



278. Other gymnosperms. There are several groups of gym- 

 nosperms, but the one to which the pines belong (the conifers) 

 is the only one that need be mentioned here. The conifers take 

 their name from the cone-bearing habit which is characteristic 

 of all members of the group. In addition to the widely dis- 

 tributed genus (Pmws) already discussed, other important 

 representatives of the conifers are the spruces (Picea), which 

 have stubby needle leaves (fig. 227, A and -S), close-set branches, 

 and pendent cones; the Western hemlock, the Douglas fir 



FIG. 226. Diagram of the seed 



of a pine, showing the embryo 



(new pine plant) inclosed within 



the food material 



At the right tip of this embryo is 



the root, and at the left are the 



seed leaves which inclose the 



small stem tip 





