STATISTICS OF METASPERMAE. 625 
It is possible also to pursue alineof investigation in regard 
to these 407 genera precisely similar to that which was followed 
out for the 106 families that are represented in the valley of 
the Minnesota. As before, in order to analyse the general 
ranges, we may group the genera under the same six divisions 
that were established for the families, namely: 
Cosmopolitan genera. 
Extratropical genera. 
Tropical and subtropical genera. 
Northern extratropical genera. 
Western Hemisphere genera. 
North American genera. 
eS to 
The grouping of the genera under these heads is with the 
same reservations as in the case of the families. As before, it 
may be necessary to enter the same genus under more than one 
head. The number of species developed in any genus is con- 
sidered to furnish the best index of its relative preponderance 
in one locality rather than another. Where, then, the species 
are particularly numerous in extratropical regions and fewer 
in tropical regions, the genus is in general set down as extra- 
tropical, and similarly in the other cases. To indicate the 
distinctive range of the genera represented in the Minnesota 
valley is the purpose of the following table: 
Genera Represented in the Minnesota Valley. 
NORTHERN 
y s R . 
EXTRATROPICAL. WESTERN HEMISPHERE NORTH AMERICA 
