300 Science of Plant Life 



trees are the Western yellow pine, Douglas fir, lodgepole pine, 

 redwood, pinon, and Sitka spruce ; and there are numerous 

 less important cedars, spruces, firs, and pines. With the in- 

 creasing demand for lumber and the gradual destruction of 

 the Eastern forests, more and more of the wood from the 

 Western forests is reaching Eastern lumber markets. The 

 seeds of the pinon are large and pleasantly flavored, and 

 formerly they furnished much of the food for the Indians of 

 California and the lower Great Basin region. 



The significance of reproduction by seeds. In a former 

 chapter (page 207) some details of the manner in which a seed 

 is produced were given, and it was pointed out that the seed 

 is a structure containing a young plant (embryo) developed 

 from a fertilized egg. The seed is better fitted to undergo 

 a period of dormancy and to carry a plant over an unfavor- 

 able period than are the small spores of ferns, mosses, and 

 fungi, or even the resting spores that are produced by certain 

 algal forms. This is because the seed contains (i) a plant 

 already partly developed, (2) a larger supply of nourish- 

 ment to start the young plant when development begins, and 

 (3) seed coats that afford better protection during the dor- 

 mant period. So efficient, indeed, is the seed in passing over 

 periods unfavorable for growth, that nearly all seeds will 

 retain their vitality for from one to several years ; and the seeds 

 of certain plants have been found to be alive after 25 years. 



Summary of the development of the plant kingdom. At 

 this point it may be well to review the most notable steps in 

 the development of plant life on the earth. These steps are : 



(i) The development from previously existing water 

 plants of land forms with epidermis, rhizoids, and other ad- 

 justments to a land environment. 



