STATISTICS OF METASPERMAE. 623 



ical regions. Of the 90 extratropical, 18 are extratropical in 

 both northern and southern hemispheres, while 17 are extra- 

 tropical only in the northern hemisphere. The character of 

 the families represented in the valley may then be summed up 

 as generally extratropical, modified by tropical. The families 

 indicate that the Minnesota valley is first of all an extratrop- 

 ical region. For their number, the Metachlamydeae contri- 

 bute the most of the distinctively tropical modification, and the 

 Archichlamydeae the least. For their number, the Monocoty- 

 ledones contribute the most of the distinctively cosmopolitan 

 element and the least of the endemic. For their number the 

 Archichlamydeae contribute the most of the distinctively extra- 

 tropical modification. These facts are in unison with the 

 notion that the Metachlamydeae, as a group, are the most 

 recent, and the Mortocotyledones, as a group, the most ancient. 

 The Monocotyledones having had a longer time of development 

 have become more widely scattered and their families are 

 therefore more generally cosmopolitan. Of the total monoco- 

 tyledonous families in the valley 61.9 per cent, are of cosmo- 

 politan range, while only 48. 3 per cent, of the archichlamy- 

 deous families are of such range. Thus in the distribution of 

 its families we find the Minnesota valley adds to the evidence 

 already derived from other sources that the Metachlamydeae 

 are comparatively recent and the Monocotyledones compar- 

 atively early in their respective emergences. 



The archichlamydeous families are par excellence the extra- 

 tropical families. Of all distinctively extratropical families 

 represented in the valley they form the large percentage of 

 77. 7 the largest percentage in the table. And of the northern 

 extratropical they form 76.4 per cent. For their number, too, 

 they are equally conspicuous as distinctively extratropical. In 

 the three great taxonomic divisions, then, we find three marked 

 distributional characters peculiar to the families. The older 

 group of the Monocotyledones is distinguished for the cosmo- 

 politan range of its families; the younger group of the Archi- 

 chlamydeae is distinguished for the extratropical range of its 

 families, while the youngest group, the Metachlamydeae, is 

 characterised by its tropical and subtropical range. The meta- 

 chlamydeous plants, then, of the Minnesota valley belong to 

 families, in general more centrally than distally located on the 

 surface of the earth; the archichlamydeous plants belong to 

 families, in general more distally than centrally located, and 

 the monocotyledonous plants belong to families, in general 



