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 1st ed. of 



(23). Bentham and Hooker: Genera Plantarum (1862-1883) . 



(24). Baillon: Hi«ioire dai Plantes (IS&r—lHSl ). 



(25). Engler and Prantl Natuerl. Pflanzenfamilien (1887-1893 ). 



