[Chap. XXVII GENERAL REGIONS AND PROCESSES IN STEMS 275 



Many of us are impressed with the superlative. Large trees, tall trees, 

 and old trees elicit considerable interest as shown by their frequent men- 

 tion in the press ( Fig. 101 ) . Some of the present-day trees are the largest 

 and have attained the greatest age of any plants that ever existed ( Fig. 



Fig. 102. Big Tree or Sequoia in the Sierra National Forest, where trees as 

 large as those pictured above are common. They are hmited to unglaciated areas 

 in the canyons of the Sierra Nevada Mountains. Photo from the U. S. Forest 

 Service. 



102). What determines the limits of age, size, and height? It would be 

 interesting to consider some of the factors correlated with size limits, 

 but space can be given here only to a few suggestions and to a summary 

 of reports of the largest trees (Table 11), What world events were in 

 progress when these trees were seedlings? 



That the stem may have potentialities of unlimited growth may be 

 demonstrated with plants, such as English ivy, that propagate readily 

 from cuttings. To do this it is necessary only to use repeatedly the upper 

 part of the same stem as a cutting and to keep it in an environment that 

 is favorable to contmuous vegetative growth. That is, it must not be 



