98 



Science of Plant Life 



over unfavorable seasons 

 like periods of cold or 

 drought. 



There seems to be no 

 limit to the length of life 

 of some perennial herbs, 

 like ferns, the May apple, 

 Solomon's seal, and cer- 

 tain grasses and mints. 

 The older parts die each 

 year, and new parts form 

 at the other ends of the 

 underground stems. The 

 plants change their loca- 

 tions slightly each year, 

 one end of the stem grow- 

 ing forward and the other 

 end dying away. There 

 is no apparent reason why 

 such plants should not 

 Hve indefinitely, perhaps 



Fig. 59. Group of California Big Trees (Se- ^ 



quota gigantea). An idea of their size and trCCS ; but UO OUC part of 



height can be gained by comparing them ^J^g pj^j^^ JJ^gg f^^ g^ J^^g 



with the man standing at the left of the picture. . 



time. 



Herbs, shrubs, and trees. Shrubs and trees have woody 

 stems. The stems of herbs lack woody tissues. Our garden 

 and field crops are all herbaceous plants. Their stems con- 

 tain no woody tissue and, for this reason, in temperate climates 

 the above-ground parts hve but a single growing season. 



The principal difference between shrubs and trees Ues in 



