16 METASPERMAE OF THE MINNESOTA VALLEY. 
gories rather than objective realities. Admitting the unques- 
tioned truth of such an objection, it seems nevertheless that 
the species and genera stand out somewhat less nebulously than 
the families, classes or divisions. Their boundaries have been 
more accurately mapped, their highways and by-ways have 
been more carefully charted and it is more admissible to de- 
mand for them at least the semblance of a stable nomenclature. 
In consequence of such considerations as these it has seemed 
unwise to insist upon strict priority in the names of families 
while maintaining it for the names of genera. This position is, 
however, not unlikely to be erroneous, or at least inconsistent. 
For reasons outlined above the genera have been determined 
under the law of priority, but this has not been insisted upon 
for the families. Under both families and genera, page num- 
bers of dated works are indexed, and such works have been 
selected as should at once put the student who refers to them 
in a fair way to gain a knowledge of the literature of any plant 
which might command his attention. The standard modern 
works have alone been cited, except in certain cases of peculiar 
historical or local interest, for, from these, proper references 
to older works may be compiled. 
Generic synonymy and limitation. Since there is little uni- 
formity in the limitation of genera, it is customary in works 
like the one in hand to follow some recognised authority, se- 
lecting the authority either at random or under the influence 
of local conditions. Bentham and Hooker’s monumental work 
(23) has during the last twenty years served as an authority to 
the English-speaking races and in less degree to others. In 
general the lines of generic limitation established in this great 
work have been adopted by the writer. In particular cases, 
however, the lines of Baillon (24) and of the monographs col- 
lected in Engler and Prantl’s not yet completed work (25) have 
been followed, thus emending the limits as proposed in the 
older volumes. 
Synonymy has been quoted to indicate the precise limitations 
accepted and all this synonymy has been properly referred to 
its original authors, and the places and dates of publication 
have been compiled. The list serves, therefore, as a partial 
date-index to Bentham and Hooker, Baillon and the German 
monographers. Genera proposed prior to the Ist ed. of 
(28). Bentham and Hooker: Genera Plantarum (1862-1883). 
(24), Baillon: Histoire des Plantes (1867—1881—), 
(25). Engler and Prantl Natuerl. Phanzenfamitien (1887-1893), 
