Rosendahl: observations on betula 



447 



clear from the two text figures, which are reproduced from camera 

 lucida drawings, but a number of points need further elucidation. 



As already stated, the only three well recognized species of birch 

 which occur in the vicinity of these hybrids are B. papyrifera, B. 

 hitea, and B. pumila var. glanditlifera. The river birch, B, nigra, 

 although found in Minnesota, is out of the question as a possible 

 parent, for it does not occur within 45 or 50 miles of the tamarack- 

 swamps where the hybrids have been found. 



KiP 1 a-b Betula papyrifera; c-d-e B. papyrifera x pumila var. glandulifera; f-g forma 

 maxima; h-i B. pumila var. glandulifera; k-1 B. lutea; m-s B. lutea x pumila 

 var. glandulifera. 



In the case of B. Sandbergi, it seems quite clear that B. papyri- 

 fera is one of the parent species because of the very close resem- 

 blance the winged nutlets of the two bear to one another. In both, 

 the wing is perceptibly wider than the nutlet and projects consider- 

 ably above the base of the styles. The leaves resemble those of B. 

 pumila var. glandulifera in size, form, serration and texture more 

 than they do B. papyrifera. In the former the number of pairs of 

 veins averages 6 to 7, in the latter 3 to 4, while the average for B. 

 Sandbergi is 5. The shrub varies from 3 to 6.5 m. in height, with 

 stems 3 to 7 cm. in diameter, and has a reddish or grayish brown 



