-+48 MINNESOTA BOTANJCAL STUDIES 



bark which does not peel into thin papery layers. There is no trace 

 of wintergreen flavor in the inner bark of either B. papyrifera or B. 

 pumila nor is there any in the hybrid B. Sandbergi. 



In the latest monographic work on the Betulaceae,* Winkler de- 

 scribes among other hybrids one between Betiila papyrifera and B. 

 pumila raised by Zabel in the Miinden Forstgarten from "American 

 Seeds" and first described by the latter in "Mitteil. der Deutsche 

 Dendrol. Gessell." 1895. This latter work is unfortunately not at 

 my disposal, and Winkler's description does not distinguish the 

 form sufficiently for me to assert whether or not it is identical with 

 the one that is found growing in Minnesota. 



That the B. papyrifera x pumila hybrid has been known to 

 European botanists and gardeners for a much longer time but 

 under another name, is asserted by Schneider," who refers it to 

 Aiton's Betula excelsa first described in "Hortus Kewensis" (3:337, 

 1789). This is contrary to the opinion expressed by Winkler, who 

 regards B. cxcclsa as a garden form of B. puhcsccns ( Regel be- 

 fore him regarded it as a sub-species of B. alba) but makes the 

 statement that its place of origin is unknown. 



From an examination of B. excelsa material from Breslau and 

 the Botanic Garden of Petrograd, kindly loaned by the Arnold 

 Arboretum, we feel certain that it is not identical with or even 

 near to the B. papyrifera x pumila hybrid as it occurs in Minnesota. 



The leaves of B. excelsa have a very characteristic rhombic- 

 ovate to ovate-cordate form and vary at the base from broadly 

 cuneate to faintly cordate. If a line is drawn across the widest 

 part of the leaf, it cuts off an upper portion which is almost always 

 an equilateral triangle, with the two legs hardly cutting into the 

 serrations, and forming two-thirds the length of the leaf. The 

 serrations are coarse and irregular. 



The leaves of the Minnesota hybrid are rhombic-ovate to obo- 

 vate, either rounded at the base or more often distinctly cuneate, 

 rounded or slightly acute at the apex and evenly though often some- 

 what coarsely serrate. The widest part of the leaf is at or near the 

 middle. The catkin, bractlet and samara of B. excelsa all resemble 

 much more closely the corresponding structures of the Betula pub- 

 esccns-verrucosa-popnlifolia group than they do our hybrid. In ad- 

 dition to this, Betula excelsa is said to be a densely branched. 



♦Winkler, Hubert, Betulaceae, Das Pflanzcnrcich, TV, 61:94. 1904. 



<* Schneider, C. K., Illustriertes Handbuch der Lauhholzkunde.l, 108-109. 1906. 



