306 PROCEEDINGS OF THE AMERICAN ACADEMY. 
little effort has been made to repeat the older citations of specimens and 
localities, which are duly recorded in Hemsley’s Biol. Cent. Am. Bot. 
Wherever possible, Bentham’s paper, the result of more than thirty 
years’ study of the genus, has been taken as a basis of arrangement. 
But his series of Rubicaules seems an unfortunate and artificial aggrega- 
tion of species without close affinities. Several of these are here placed 
with the Schrankioidee, and M. Berlandieri is referred to what is 
believed to be its natural position as a variety of JL asperata. It is 
doubtful whether Bentham ever saw M. Ervendbergii. At all events 
he did not recognize what is now evident, namely, that it was founded 
upon two distinct plants. 
The construction of a satisfactory key to the species of Mimosa is 
well nigh impossible. Except in the number of their stamens the 
flowers are too uniform to furnish many good characters. The inflores- 
cence passes gradually from capitate to spicate, the number of leaflets 
varies astonishingly upon the same individual, and the spines are singu- 
larly inconstant, being well developed or obsolete in plants which appeat 
in all other respects identical. Therefore the key here offered, although 
the result of considerable study and experimentation, must be used with 
due caution. M. albida, acanthocarpa, and biuncifera appear to be 
the types of polymorphous aggregates of intergrading forms. Aside, 
however, from these species and several of their close allies, the species 
within the limits of the present paper are pretty clearly marked and 
show little tendency to intergrade. 
Besides the material in the Gray Herbarium, the writer has been 
kindly permitted to examine and borrow from the material of Mimosa 
the Herbarium of the N. Y. Botanical Garden. Mr. John Donnell 
Smith has lent his rich representation of the Central American Sensi- 
tive, and Dr. J. N. Rose of the U. S. National Museum, has sent - 
examination a large number of most interesting forms from Mexico 
collected chiefly by himself and Mr. Nelson, and containing several neW 
and well marked species. Further material has also been sent to oe 
writer from Lower California by Mr. and Mrs. T. S. Brandegee, from 
Honduras by Dr. Gustavo Niederlein and from New Mexico by ge 
Mulford. Upon request several specimens have been examined a0 
compared by the staff of the Royal Gardens at Kew. For all of these 
favors, which have contributed much to the completeness of the present 
revision, the writer here expresses grateful appreciation. 
_ The generic limits ascribed to Mimosa in this paper full 
with those of Bentham and other recent writers, so that it is 
y coincide 
