SUCCESSION 273 
tion just described, is nicely illustrated by the balsam-spruce formation at 
‘Minnehaha. Of the initial gravel slide stage, the relicts are Vagnera stellata 
and Galium boreale, the one modified into Vagunera leptopetala, and the 
‘other into G. boreale hylocolum. The thicket stage is represented by Holo- 
discus dumosa, greatly changed in form and branching, and in the shape 
and structure of the leaf. The most striking relict of the aspen formation 
is the facies itself, Populus tremuloides. The tall slender trunks of dead 
aspens are found in practically every balsam-spruce forest. In many places, 
living trees are still found, with small, straggling crowns, which are vainly 
trying to outgrow the surrounding conifers. Of the aspen undergrowth, 
Fig. 71. Relict spruces and aspens, showing the character of the suc- 
cession immediately preceding the burn succession now developing. 
Rosa sayu, Heiianthella parryi, Frasera speciosa, Zygadenus elegans, Cas- 
tilleia confusa, Gentiana acuta, and Solidago orophila remain more or less 
modified by the diffuse light. It is still a question whether the aspen stage 
passes directly into the balsam-spruce forest, or whether a pine.forest inter- 
venes. The presence of both Pinus ponderosa and P. flexilis, which are 
scattered more or less uniformly through the formation, furnishes strong 
evidence for the latter view. 
The lifetime of forest and thicket stages of successions is ascertained by 
counting the annual rings of the stumps of facies. This is a perfectly feasible 
