TREES AND SHRUBS 165 



conditions, there are a few tribes of deciduous 

 trees that make at least a commendable effort 

 to rival them. 



Notable among these is the birch. But the 

 beech, oak, maple, hickory, and walnut also have 

 representatives that are able to withstand the 

 winter in regions where the mercury freezes. 



All of these have a certain importance as 

 ornamental trees, but in the main they are 

 valued rather for their timber, and we have dealt 

 with them when we spoke of forest trees. 



There is a considerable company of trees of 

 less hardy character that nevertheless are resist- 

 ant enough to thrive in the streets, parks, and 

 gardens of our Northern States if given a cer- 

 tain amount of protection, even though some of 

 them could not make their way in the wilds 

 in competition with the hardy tribes just 

 mentioned. 



These trees are less hardy than the others, 

 presumably because they migrated a little more 

 rapidly in the old days of changing climates and 

 kept far enough away from the ice sheet to be 

 able to retain something of their taste for tropi- 

 cal conditions. They not only retained the 

 broad leaf system, but some of them also re- 

 tained or developed the habit of bearing hand- 

 some flowers — a habit that would have served 



