414 



STRUCTURE AND LIFE HISTORIES 



observation discloses the fact that these are really pseudo- 

 whorls, since the branches do not emerge at precisely the 

 same level on the trunk, as in true whorls. Both because 

 they are older, and because they receive less light, the 



Fig. 305. — Elm tree {Ulnms americana), showing deliquescent trunk. 



lower branches are longer, and the gradual decrease in 

 length from below upward, combined with the excurrent 

 habit of the trunk, gives the tree a pyramidal outline when 

 it grows free in the open. This shape is modified by 



