16 TREES OF THE NORTHERN UNITED STATES 
trunk form another distinctive feature. Thus the up- 
ward sloping branches of the Elm form a striking con- 
trast to the horizontal or downward sloping branches of 
the Sour Gum, or, better still, to certain varieties of Oaks. 
When the main trunk of a tree extends upward 
through the head to the tip, as in Fig. 3, it is said to be 
excurrent. When it is soon lost in the division, as in 
Fig. 4, it is said to be deliquescent. 
