tort] COOPER—LAYERING AMONG CONIFERS 375 
4. A balsam growing in a large rock crevice at the forest edge 
On an exposed shore had several layered branches, erect at tip, 
through the soil at the general level of the ground. Several similar 
branches, at about the same elevation but in line with the crevice, 
descended into it somewhat, but their ends were erect, radially 
symmetrical, and perfectly treelike. Since the crevice was a foot 
wide and contained no soil, no roots were formed in this case, and 
these branches remained entirely dependent upon the tree. 
Aside from the balsam, layering was less frequently observed 
in every one of the coniferous trees that occur upon Isle Royale. 
It was fairly common in the case of the black spruce, perhaps being 
favored by the pronounced droop of the lower branches of that 
species. The black spruce occurs sparingly in the upland forest, 
and in this habitat the layered branches were identical in behavior 
with those of the balsam. Black spruces and tamaracks growing 
in bogs were found to layer abundantly through the rapidly grow- 
ing sphagnum. Specimens of white spruce were found upon nearly 
bare rocks, whose lowest branches, covered with a thin mantle of 
humus, had developed the layering habit to such an extent that 
the parent had become entirely surrounded by a group of daughter 
trees. Similar groups were seen in the case of arbor vitae growing 
IN a river swamp. 
Ill. Conclusions from data presented 
From the material here presented we gather that the habit of 
natural layering among coniferous trees is common and widely 
distributed, though its importance appears to have been generally 
overlooked, at least in this country; that it is particularly character- 
istic of the closely related genera Picea and Abies, but is found in 
many other genera, among which are Larix, Thuja, Pinus, Pseudo- 
tsuga, Chamaecyparis, and Cryptomeria; that it is most prominent 
in northern and mountain regions, and that it occurs more fre- 
quently and attains more striking development with increasing 
latitude and altitude; that its best development is found at the 
extreme limit of the forest—the arctic tree line and the mountain 
timberline. 
The general region of its occurrence is practically that of conifer 
