78 



CONTRIBUTIONS FEOM THE NATIONAL HERBARIUM. 



rather superficial examination, and, one would say, of no compariwon whatever. 

 The total absence of those transverse rugosities and also of the small resiniferous dots 

 that mark tlie body of the more genuine species of tlie genut^, are to my mind more 

 significant differences. Another distinction, and one wliich I note as more important 

 than the absence of a wing is, that, wliile the seed-bearing i)art of the typical Ptelea 

 samara ih thin, po thin as to rise but a little above the wing on either face, the nut of 

 P. ajytcraiB thick and strongly double-convex. Lastly, this nut is deliiscent. Set 

 upon edge and struck with a tack hammer, it splits into two valves as readily as an 

 almond, whereas the seed-bearing body of the samara of ordinary Ptelea can be torn 

 open but with difiiculty, and at any other part with less difficulty than along the 

 edges where the sutures ought to be. 



