Vol. 36 



BULLETIN 



No 8 



OF THE 



TORREY BOTANICAL CLUB 



AUGUST, 1909 



The western American birches 



Bertram T. Butler 



The present paper aims to define and characterize the birches 

 of western North America, about which very little has heretofore 

 been written and which have been in more or less confusion as to 

 their identification. After several seasons' work in the field and 

 with the collections in the herbarium of the New York Botanical 

 Garden and those of the College of Pharmacy, Columbia Univer- 

 sity, I have concluded that the birches of the West are mostly dis- 

 tinct from those of the East, only a few of the eastern species 

 reaching the regions west of the Great Plains. The idea main- 

 tained by many writers of regarding the western forms as varieties 

 or ev^en as hybrids of eastern species has no scientific basis, the 

 majority of the confusing varieties and hybrids having been proposed 

 rather as a conjecture based upon a few superficial characters, and 

 without proper study of living material or understanding of habitat 

 and distribution. 



+ 



While several of the species as described below show consid- 

 erable variation, it seems more practical to group about a leading 

 type all forms that cannot be clearly characterized than to give 

 them varietal rank. Forms sufficiently distinct to warrant recog- 

 nition have been regarded as species. 



The illustrations are from drawings by the author and give in 

 each instance the typical leaf-form, actual size, outline of the fruit- 

 ing ament, actual size, and outline of the fruiting bractlet enlarged 

 four diameters. Western forms have been given 



in cases where 



West 



[The Bulletin for July, 1909 (36 : 353-420. //, 2j) was issued 14 Au 1909.] 



421 



^ 



