Mr. Douglas notes the curious and very interesting fact that in the Rocky Mountains the aspen only seems to make one in forest succession after the forest fire has been over the ground. The following from the Gardeners' Chronicle also has a similar bearing on this point:

"The aspen trembles all through Europe. It may have commenced its curious habit in the Caucasian range, where it is still a prominent tree, but historically it has always been dispersed over Turkey and Russia as far as the Frozen Ocean, and there is nowhere such a trembling of aspen leaves as in the woods around Moscow, where innumerable seedlings sprang up after the conflagration of 1813. The aspen is found in the bogs of Denmark at all depths, while the alder, birch and hazel do not occur below the oak level. Like the Scotch fir, therefore, it is one of the primaeval trees of Europe. It is also a native of the woods of Inver-cauld, near Braemar, where it ascends to a height of 1,600 feet. It travels into Sutherlandshire, loves moist situations and woods, overhanging the Highland lochs. The margin of Loch Katrine and the islet of the ' Lady of the Lake ' are its favorite sites."