60 



SILVA OF NORTH AMERICA. 



ULMACEiE. 



composed of twenty or thirty layers of annual growth. The specific gravity of the absolutely dry wood 

 is 0.5294, a cubic foot weighing 32.99 pounds. 



The genus is not known to possess useful properties. 



The generic name preserves the memory of Johann Jakob Planer/ a German botanist and physician 

 of the last century. 



The genus is now represented by a single species.^ 



(1743-1789) 



inhabited 



his scientific studies at Berlin and Leipzig, and in 1779 was appointed during the tertiary epoch (Zittel, Handh, Palceontolog. ii. 472) ; and 



Professor of Medicine in the University of his native city, in which in North America traces of several species of Planera found in the 



he afterward filled the Chairs of Botany and Chemistry, Planer Upper and Middle Miocene rocks show that it once existed in the 



was the author of several works on Botany and Rural Economy, central Rocky Mountain region of the continent and in Alaska 



including a catalogue of the plants growing in the neighborhood of (Lesquereux, U, S. Geolog, Surv. vii. 189, t. 27, f . 4-6 ; viii. 161, t. 



Erfurt and papers on silviculture. 29, f. 1-13, t. 44, f. 10 [Foss. FL Western Territories^ ii., iii.l). 



