642 METASPERMAE OF THE MINNESOTA VALLEY. 
metachlamydeous genera 12.5 per cent. are limited in their 
range to the western hemisphere. This percentage does not 
include, however, the results of the succeeding table, for in 
every case distinctive not total range, is given. This was 
explained above for the families. The last table of the series 
follows: 
10. North American Generic Element. 
Per cent. of all) North American 
North American. | per cent. of each. 
Monocotyledones... .. 14 21.9 13.3 
Archichlamydeae.. .. 23 35.9 13.1 
Metachlamydeae...... 27 43.2 13.2 
Total North American 64° edwwwunceera wake Calacaae oned eoamewean 
North American per 
cent. of all genera.... 158) ‘lenge sg eteeuseseuel eases oes icmaiemniea 
The figures of the last table indicate two facts concerning 
distribution, both of which are important. By the slight varia- 
tion in the last column from the mean of 13.2 per cent. it will 
be seen that, so far as the valley of the Minnesota and its Meta- 
spermae can be placed in evidence, there is about an equal 
tendency in each of the three taxonomic groups to develop 
endemic genera. The last column of figures serves to strengthen 
our belief that the Metachlamydeae are the youngest of the 
three groups,for while the opportunity for developing endemic 
genera is no better in this group than in the other two, we find 
upon examining the figures of the second column that the 
Metachlamydeae include by far the larger per cent. of the en- 
demic genera. The apparent explanation of this fact by the 
different length of time that has sufficed for distribution in and 
out of the continent, in the case of the three groups of un- 
equal age, is even more clearly developed by the evident inad- 
missibility of attributing this difference of range to any in- 
herent quality of the groups in question. 
An examination of the genera may also be conducted to de- 
termine the North American developmentof each. In the next 
table the genera are classified as northern, southern, eastern 
and western. Some explanation of this grouping may be 
