SCIENTIFIC PAPERS. 
A REVISION OF THE AMERICAN LEMNACEAE OCCURRING NORTH 
OF MEXICO. 
BY CHARLES HENRY THOMPSON, 
Hitherto no revision of the Lemnaceae for the North 
American continent has been published, though a number of 
botanists have made some special study of the order at 
various periods. In 1839, Schleiden* published a mono- 
graph of the then known species in which occurs reference 
to a few of the American forms. In 1867, Austin f pub- 
lished in Gray’s Manual the species of the northeastern 
United States. The year following Hegelmaier’s ¢ general 
monograph appeared, in which are recorded the descriptions 
of many species from America previously unknown. Con- 
temporaneously with these latter gentlemen Dr. Engelmann 
of St. Louis, and Dr. Torrey of New York, made careful 
studies of the species occurring in their respective localities, 
as well as the abundant material sent them from other 
points, the results of which were published from time to 
time in the Bulletin of the Torrey Botanical Club. In 
1878 Hegelmaier{ revised the order for Brazil, giving 
further knowledge of some species that occur also in 
North America. In 1895, he |] again published a review 
*Schleiden, M. J. Prodromus monographiae Lemnacearum oder 
Conspectus generum atque specierum. Linnaea, 183 385-392. 1839. 
¢ Austin, C. F, Lemnaceae.—Gray, A., Man. Bot. 478. 1867. [5th ed.] 
t Hegelmaier, Friedr. Monogr. Lemnaceen. May 1868. 
{ Hegelmaier, Friedr. Lemnaceae.—Martius, Fl. Bras. 82: 1-24. Feb. 
1878. 
|| Hegelmaier, Friedr. Systematische Uebersicht der Lemnaceen. 
Engler’s bot. Jahrb. 21°: 268-305. Jan. 1895. 
Separates issued Nov. 1, 1897. 1 
