EVERGREEN TREES AND SHRUBS. 
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not likely that our northern sun can be too much for it, unless some 
preceding cause exists for abnormal sensibility to heat. The tree 
is found at an elevation of from six to ten thousand feet above the 
level of the sea, and “ prefers the more open and cheerful aspects 
of the mountains.” Such an elevation even in the tropical latitude 
of 27° to 29° insures a comparatively temperate summer climate 
and severe winters, but does not diminish greatly the blistering 
power of the sun’s rays, as those know who have travelled on the 
glacier heights of the Alps. We cannot therefore believe that full 
exposure to the sun will of itself be found prejudicial to the health 
of the Bhotan pine, but think it much more likely that the source 
of its weakness in this country is simply a density of air quite 
different from that breathed by the tree at an elevation of six and 
ten thousand feet above the sea ; and this alone may produce what 
Mr. Sargent terms “a determination of sap to the head” — or 
vegetable apoplexy. It will therefore be a simple matter for 
patient experimenters to determine to what extent the Bhotan pine 
may be acclimated in the United States. 
We believe that much may be done by selecting seed from trees 
that exhibit the greatest vigor in localities the most exposed to sun, 
wind, and cold, at the lowest elevation where the tree flourishes. 
It is quite probable that most of the seed imported into England 
has been obtained from the great trees of the valley-forests nearest 
to the English stations. With seed from the most weather-tried 
trees, it seems reasonable to suppose that a hardier stock of this 
pine may be grown, and from among the progeny of such seed 
some specimens of sufficient hardiness to insure their healthy growth 
in the United States. We have not heard whether any experiments 
have been tried in grafting the P. excelsa on different pine stocks to 
learn the effect, if any, on the subsequent growth. By grafting 
scions from the same tree on the roots respectively of the white, 
the Austrian, and the Scotch pines, it may readily be ascertained 
whether anything can be gained in that direction. If the P. excelsa 
scion will take readily on the Austrian pine stock, very beautiful 
effects may be produced by cutting off the leader of the latter from 
eight to twelve feet above the ground, and inserting grafts of the 
former, without marring the side branches of the stock. The 
