THE PLANT BODY 



21 



SPREADING TREE TYPES 



The elm. In trees of the spreading type, like the elm, poplar, 

 oak, and hickory, the same general plan of development can be 

 traced as that outlined for the pine, except that the terminal 

 bud of the main 

 axis is replaced 

 by a lateral bud 

 after a few years, 

 so that no main 

 central excurrent 

 trunk is contin- 

 ued throughout 

 the life of such 

 trees. In the elm 

 the terminal bud , 



is replaced each I 



season by a lat- 

 eral bud, which 

 produces a main 

 central excurrent 

 trunk for a few 

 years (Fig. 11, e). 

 Ultimately, as in 

 all such trees 

 of the spreading 

 type, a few lateral 

 branches gain the 



FIG. 11. Growth of the American elm, an illustration of 

 the spreading type of trees 



ascendancy and The letters from left to right show several stages in the de- 

 form all of the velopment of the elm. The ultimate form is determined by 

 body plan, the method of bud growth, and pruning effects. 

 The corresponding letters on each figure indicate the vigor- 

 ous (and so successful) branches produced each season. For 

 further discussion consult the text 



spreading crown 

 of the adult tree 



(Fig. !!,/> 



So long as the central axis continues to grow in length, its 

 method of growth, as well as that of the vigorous lateral branches, 

 follows the general plan already outlined for the pine. The ter- 

 minal twigs at the ends of the main branches produce each year 



