STATISTICS OF METASPERMAE. 643 
necessary. Preponderance of species in one of the regions 
over the opposite region is taken as the index of range. 
The 95th meridian W. of Greenwich is adopted as the line di- 
viding the eastern from the western half of the continent, and 
the 45th parallel of N. latitude as the line dividing the north- 
ern from the southern region. Ifthenina given genus a greater 
number of species occur north and east of the dividing lines 
than south and west, such a genus is entered as northern and 
eastern, in the table. No attempt at hairsplitting distinctions 
has been made, and genera developed pretty evenly in all parts 
of the continent are entered in each of the four groups. Very 
commonly a genus will be entered in three groups. The groups 
of three which are most common are the north-east-west, the 
south-east-west and north-south-east groups. It is believed 
that by such a comparatively elastic method of entry more ac- 
curate results will be obtained than if one were to attempt for 
each genus to strike such a demarcation line that it could fall 
into but two groups. Again, in the case of genera either 
monotypic or with very few species, the numerical test must be 
abandoned. In its place is adopted the specific range and the 
comparative frequency of individuals on different sides of the 
demarcation lines. From these considerations it will be seen 
that the north-south-east-west group of genera is of the most 
generally distributed genera while the south-east or north-east 
group and others of similar construction are the least gener- 
ally developed in the North American continent. Large de- 
velopment of range may however, and often does, exist to- 
gether with small development of species, or vice versa. With 
so much of emphasis upon the elasticity of grouping the table 
may be presented. 
C. Table Illustrating Continental Development of Genera 
Represented in the Minnesota Valley. 
NORTHERN. SOUTHERN. EASTERN. WESTERN. 
Typh 
TY DHS) ces eccante caine eeisnin TY DH Bsiiscis: jess tie eceaw Typha TY DAA ix scnceemaetoirs 
Sparga| niaceae. | 
SPAPPAMTOM woes 3: scence |p sneneie xs camesesesacees Sparganium.........] Sparganium..... ... 
: Potamog|etonaceae. ‘ 
POtAMOPStOD ss cssecdece|esceee ders eisosieicacse|, POtCAMOBROTOR: ssesad|eesuine cram senedieremnerie 
Lanichellia......»s.+-.--| Zanichellia.........- Zanichellia.......... Zanichellia.. 
Naja\daceae 
dhuids Sointasi sister a eee NAJ OS) csi neice zee | INGIAS Sa cecimne uate as| < 
Junea|gineae. 
Trig LOCH intigen js x sivstviogjal| sawittane Sioid doreieeieaege-waee Triglochin........... Triglochin.... 
Scheuchzeria:. vi: ss csvecaullacciastesing wae sear earns Scheuchzeria........ Scheuchzerla........ 
Alism|aceae, 
Alisma Pere te ee eee ee intense wee Alisma,......... ...05 
Tcarastnacara ates atendeasaiies ss giatsieiD sian Sagittaria.......... | Sagittaria........... 
