EVERGREEN TREES AND SHRUBS. 535 



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 



