LUTHER BURBANK 
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 resistant 
enough to thrive in the streets, parks and gardens 
of our northern States if given a certain 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 tropical con- 
ditions. They not only retained the broad leaf 
system, but some of them also retained or devel- 
oped the habit of bearing handsome flowers—a 
habit that would have served small purpose for 
the conifers, since insects could not thrive in cold 
regions where they remained to battle with the 
elements, 
Doubtless the most interesting of these trees 
that escaped destruction by flight, and the one that 
has maintained most fixedly the traditions of the 
Mesozoic era is the tulip tree (Liriodendron). 
This beautiful tree, with its unique broad 
glossy leaves and handsome flowers is now the 
lone representative of its genus. One species alone 
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