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CONTRIBUTIONS FROM THE GRAY HERBARIUM OF 
HARVARD UNIVERSITY, NEW SERIES, No. XIIL 
By B. L. Rosrnson. 
Presented March 9, 1898. 
I.— REVISION OF THE NORTH AMERICAN AND 
MEXICAN SPECIES OF MIMOSA. 
Tue 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 Synoptical 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, Dug’s, Hartman, 
and Lloyd, are all of later date. They have added a wealth of new 
naterial, but it has been identified at different times and places and, as 
's 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. 
