[Chap. XXVI FORMS AND EXTERNAL FEATURES OF STEMS 255 



California have three such intra-seasonal cycles of growth. The twigs on 

 young trees of the rubber plant ( Hevea ) in Brazil may have as many as 

 eight cycles of growth in one year. In the latitude of Ohio, a second 

 elongation of shoots on elms is usually evident during the latter half of 

 June, and frequently a third extension appears in August. In Europe 

 these shoots have been called "St. John's shoots" and "Lammas shoots" 

 because of their coincidence with the festivals of St. John's Day and 

 Lammas Day. 



Recognition of trees by twig characters. To those of us who are in the 

 habit of recognizing common trees by leaf characters, it is at first sur- 

 prising to find that identification can be just as certain with twig charac- 



FiG. 90. Bud and twig characters of a few woody plants: A, tree of heaven 

 (Ailanthus) ; B, tulip tree (Liriodendron) ; C, hazel (Conjlits) ; D, red oak {Qiier- 

 cus); E, white heart hickory {Carya alba); F, bitternut hickory {Canja cordi- 

 jormis) . 



ters (Fig. 90). Trees may be recognized by types of branching, which 

 are usually more obvious in the absence of leaves. A critical comparison 

 of the bark, buds, lenticels, and pith of our common trees soon enables 

 one to select a few simple distinctive characters by which these trees 

 may be readily identified during the winter. The prevailingly opposite 



