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52 CONTRIBUTIONS FROM THE NATIONAL HERHAKIUM. 



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its ^\inf?cd margin, the seed-bearing body is central in some and vari- 

 onsly eccentric in perluips the ureater number. This body of the 

 fruit, in its germinal stage in the flower— that is, as an ovary— is 

 raised on a gynophore or stipe, which stipe, lengthening afterward^s 

 with the growth of the wing in which it is merged, yet appc^irs on the 

 surface of the wing below the body, just as the lengthened style is 

 manifest as a line ruiming along the surface of the wing above the 



body. I have expressed the centricity of the l)ody by the phrase, 

 ''style and stipe equal," its eccentricity in the din^ctioii of the l)ase by 

 "style longer 'than the stipe," its nearer approach to summit— a rare 

 condition — by "style shorter than the stipe." 



Ea(;h one of the three natural groups of Ptelea here outlined has its 

 own geographical limits, and nothing in this study has more deeply 

 interested the investigator than tlie geographic distribution of the 



groups. 



The principal one of the three— that is, the group richest in species 

 and of ]nost extended and varied range, the group with chestnut-brown 

 twigs and prevailingly glaucesccnt or bluish-green foliage— is dis- 

 persed throughout !it least middle and nortluuii Mexico, as well as 

 adjacent southern Arizona, New Mexico, and Texas, thence northward 

 along the .Mississippi to the Great Lakes, and everywhere eastward to 



the Atlantic, 



A second group,. that with twigs almost white and foliage yellow 

 green, forms a belt wdiich runs eastward from northwestern Arizona 

 alone- tiu'. Grand Canyon of the Colorado, there and in southei'u Utah 

 forming a curious sort of boundar}^ to the distribution of Pielea north- 

 ward in that part of the country, the belt i-eaching its eastern limit in 

 the canyon of the Arkansas in southern Colorado, from which point, 

 and still as a narrow belt, it runs down the Kio Grande to the neigh- 

 borhood of El l*aso, Texas ; the belt in this x^art of its course not Hniit- 

 ino- but intcrsectinir the ofreat main division of the genus. 



- .J^^K. Amv..,,v V...*..p, ^..^ ^ 



The third group, that with cinnamon-colored twigs, a quite peculiar 

 hue and venation of foliage, and narrow-winged or even wingless 

 samaras, extends in also a narrow belt, ruiuiing northward and south- 

 ward west of the crest of the Sierra Nevada, between northern Cali- 

 fornia and at least the middle of the Lower California peninsula. 



Of the lifty-nine species here defined, not quite all are new, two or 

 three of them having been indicated somewhat recently by Dr. Small 

 [uid Mr. Heller, these belonging to the Texan district. 



Among the new ones are several of very recent detection in iMexico, 

 having come to hand only after this paper was nearing completion. 

 One of these w^as distributed bv Mr. rringle under tue name Dr. 

 Rose hud assigned it. The others Dr. Koso had himself collected 



and determined to be new. He has chosen that these should all l)e 

 incoi'poratcd into this monot^n*aph, I'ather than give them separate 

 place among \m own miscellanies of Mexican botany. 



