4Ij] FLORA OF BOULDER, COLORADO 265 



APPENDIX A. 



Tidestrom in the Am. Midi. Nat. 2, 35, has described as a new 

 species this aspen under the name of P. aurea Tidestrom, with 

 the remark that it forms forests throughout Colorado, Utah, and 

 adjoining territory. But the differences relied upon to separate it 

 from Michaux's species seem to me to be at most varietal, and 

 hence I prefer to call the Colorado tree P. tremuloides aurea (Tide- 

 strom) Daniels. See page 98. 



