CONTRIBUTIONS FROM THE GRAY HERBARIUM OF 

 HARVARD UNIVERSITY, NEW SERIES, No. XIII. 



By B. L. Robinson. 



Presented March 9, 1898. 



I. — REVISION OF THE NORTH AMERICAN AND 

 MEXICAN SPECIES OF MIMOSA. 



The greater part of our North American species of Mimosa barely 

 attain our southwestern borders. They are the northernmost represen- 

 tatives in the New World of a large and difficult chiefly tropical group, 

 and their affinities must accordingly be sought among more southern 

 forms. In revising for the Si/>ioptical Flora the North American 

 species of the genus, the writer has, therefore, been constantly com- 

 pelled to trace their southward extension and study their relationships 

 among the Mexican and even Central American species. This has 

 necessitated the examination of critical and imperfectly identified mate- 

 rial to such an extent, that a general revision of the Mexican and 

 Central American, as well as the North American species, has seemed 

 the simplest solution of the difficulties. Bentham's well-known mono- 

 graph* of the genus, — which must always stand as one of the classics 

 of botanical taxonomy, — is as clear and excellent as ever, but has 

 become somewhat antiquated by nearly a quarter of a century of unpre- 

 cedented activity in exploration. The large and rich collections of Messrs. 

 Pringle, Palmer, J. Donnell Smith, Nelson, Rose, Brandegee, Mills- 

 paugh, L. C. Smith, C. L, Smith, Pittier, Conzatti, Duges, Hartman, 

 and Lloyd, are all of later date. They have added a wealth of new 

 material, but it has been identified at different times and places and, as 

 is natural, with varying degrees of accuracy ; so that in this, as in every 

 other large group, the true results of modern exploration can only be 

 brought to light by revision and monographic study. The specimens 

 cited in the following synopsis are chiefly those of recent collectors, and 



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* Trans. Linn. Soc. xxx. 388-441. 



