STATISTICS OP METASPERMAE. 617 



It will be necessary to observe one or two points in this 

 division. In the firsfc place it must be recognised that not all 

 of the families in any of these groups are of equivalent distri- 

 bution. In Group A, for example, have been included such 

 families as are represented in both tropical and extratropical 

 regions of both eastern and western hemispheres. A family 

 of which the range answered to such a description might nev- 

 ertheless be very much more limited in its distribution than 

 one which might be found in almost every continent or island 

 as, for illustration, the Juncacece. The groups are therefore 

 intended to be and are somewhat elastic. Again, it is some- 

 times thought advisable to include the same family in two, or 

 even three groups, in order to give the proper notion of its 

 range. For example, the Sarraceniacece includes three genera, 

 Sarracenia, Chrysamphora and Heliamphora. The first two are 

 limited to North America, one being Atlantic, the other Pacific. 

 The third is found in British Guiana. Under these conditions 

 of North American preponderance it seems proper to enter the 

 Sarraceniacece as North American. But since a genus is devel- 

 oped in South America it seems proper, too, to enrol the fam- 

 ily among the Western Hemisphere forms. Third, it will be 

 noticed that Cosmopolitan families belong also to the next five 

 divisions; Extratropical families include also the Northern 

 extratropical. North American families are included in the 

 Western Hemisphere group. Evidently, then, the general 

 intent of the classification into groups is to give not total 

 range, but distinctive range. We see, then, how the Juglandacece 

 may be classed as Northern Extratropical, while the Saxifraga- 

 cece, being represented also in the southern hemisphere, are 

 more properly placed under the wide group of Extratropical 

 families. 



The following table will indicate the distinctive range of 

 Minnesota valley families: 



