306 PROCEEDINGS OF THE AMERICAN ACADEMY. 



little effurt 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 Schrankioidece, and M. Berlandieri is referred to what is 

 believed to be its natural position as a variety of M. asperata. It is 

 doubtful whether Beutham ever saw M. Ervendhergii. 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 appear 

 in all other respects identical. Therefore the key here offered, although 

 the result of considerable study and expeiimentation, must be used with 

 due caution. M. albida, acanthocarpa, and hiuncifera 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 

 sho'vv 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 3Hmosa in 

 the Herbarium of the N. Y. Botanical Garden. Mr. John Donuell 

 Smith has lent his rich representation of the Central American Sensi- 

 tivce, and Dr. J. N. Rose of the U. S. National Museum, has sent for 

 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 the 

 writer from Lower California by Mr. and Mrs. T. S. Brandegee, from 

 Honduras by Dr. Gustavo Niederlein and from New Mexico by Miss 

 Mulford. Upon request several specimens have been examined and 

 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 fully coincide 

 with those of Bentham and other recent writers, so that it is needless 



