98 



Science of Plant Life 



over unfavorable seasons 

 like periods of cold or 

 drought. 



There seems to be no 

 limit to the length of Hfe 

 of some perennial herbs, 

 Hke 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 

 live indefinitely, perhaps 

 longer than the oldest 

 trees ; but no one part of 

 the plant lives for a long 

 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 live but a single growing season. 

 The principal difference between shrubs and trees lies in 



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

 quoia gigantea). An idea of their size and 

 height can be gained by comparing them 

 with the man standing at the left of the picture. 



