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CONTRIBUTIONS FROM THE SHAW SCHOOL OF BOTANY. 

 No. 6. 



North American Rhamnacese. 



By William Trelease. 



Presented Apr. ij, 1SS9. 



I am indebted to Mr. Watson, Dr, Vasey, Dr. Britten, Mrs. 

 Curran, Mr. Martindale, and Captain J. D. Smith, for the privi- 

 lege of using the large collections which they own or control, in 

 the study of this Order, begun two years ago. More recently, 

 I have been permitted to look through the herbaria of Kew Gar- 

 dens, the British Museum, Berlin, and Copenhagen, where some 

 additional light has been obtained. Specimens clearing up doubt- 

 ful points, or indicating erroneous conclusions, are requested, and 

 will be gratefully received. 



According to Bentham & Hooker (Gen. i. 372), there are 

 about 430 species of Rhamnaceae, distributed through the tem- 

 perate and warmer parts of both the Old and New World. Du- 

 rand (Index Gen. Phanerog. 6S) has since increased the number 

 of seemingly good species to about 475- Torrey and Gray (Fl. 

 N. Am. 1838, i. 359) describe 34 species from our region. Wat- 

 son (Bibl. Index, i. 163) enumerates 47 as belonging to our flora. 



With the exception oi RhanDiiis cathartica ^ which has escaped 

 from cultivation, our species are peculiai'ly American, either 

 belonging exclusively to our flora, or extending on the one hand 

 into that of northern Mexico, and on the other into the tropical 

 Gulf region. 



The Rhamnaceaj, as arranged by Bentham and Hooker (Gen. 

 i. p. xi.), belong in the Cohoit Celastrales, of discifloral Polype- 

 tala;, which (for our flora) also includes the Celastracefe and 

 AmpelidejE (or Vitaceae). All, so far as we are concerned, are 

 woody plants with small flowers having a rather prominent re- 

 ceptacular disk, under or at the margin of which the stamens are 



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