Roscndahl: observations on betula 459 



EXPLANATION OF PLATE XLIX 



Photo-micrographs of pollen from mature anthers, stained with acid 



fuchsin and mounted in lactic acid. All figures magnified about 200 times and 



photographed to the same scale. 



Fig. 1. Betula papyrifera. Pollen practically all good. 



Fig. 2. Betula Sandbergi (B. papyrifera x pumila var. glandulifera). Pol- 

 len with about 45 per cent defective grains. 



Fig. 3. Betula pumila var. glandulifera. Pollen all good. 



Fig. 4. Betula lutea. Pollen practically all good. 



Fig. 5. Betula lutea x pumila var. glandulifera. Pollen with about 2)2) per 

 cent defective grains. 



Fig. 6. Betula lenta. Pollen all good. 



Fig. 7. Betula Jackii (B. lenta x pumila). Pollen with about 25 per cent 

 defective grains. 



