STATISTICS OF METASPERMAE. 721 
From the nine tables preceding it will be observed that the 
SE. element, forming 32.5 per cent. of the total species, is the 
largest numerically, while the NE., with but 2.3 per cent. of 
the total species, is the smallest. The NEW. element, form- 
ing 16.7 per cent. of the total. is larger than the SEW. 
element, which forms but 8.5 per cent. of the total. General 
east and west ranging is more characteristic, then, of the 
northern than of the southern element, and this fact is quite 
in accord with the greater dispersion of the northern floral 
elements. Of the NEW.element the actual percentages of Mono- 
cotyledones and Archichlamydeae are in excess of the Metach- 
lamydeae percentages, while in the SEW. element the re- 
verse is the case. These range-elements form similar per- 
centages of the taxonomic groups. Of the Monocotyledones 
and Archichlamydeae, respectively, 21.4 per cent. and 17.2 per 
cent. are placed in the NEW. element, while of the Metach 
lamydeae only 11.5 per cent. are so enrolled. On the other 
hand, in the Metachlamydeae 13.1 per cent are entered as 
SEW., while of the Monocotyiedones and Archichlamydeae re- 
spectively 6.6 per cent. and 5.8 per cent. are so entered. The 
Archichlamydeae with 27.0 per cent. form, however, a larger 
portion of the total SEW. element than do the Monocotyle- 
dones with 22.0 per cent. 
The two vertically distributed groups are somewhat more 
difficult to understand. The NSE. is in distinct preponder- 
ance over the NSW., having 13.6 per cent. of the total 
against 3.5 per cent. This is on account of the general eastern 
preponderance over western. Of the NSE. element the 
Metachlamydeae with 19.8 per cent. are behind the Monocoty- 
ledones with 36.6 per cent. and the Archichlamydeae with 40.9 
per cent. Of the NSW. element, the Metachlamydeae are 
ahead with 48.7 per cent. against 38.4 per cent. of Archich- 
lamydeae and 12.8 per cent. of Monocotyledones. This differ- 
erence between the two vertical elements is probably to be re- 
ferred to the lateral influence of the mountain ranges east and 
west of the Minnesota valley and to the angle made by the two 
principal continental trenches—the Mississippi valley and the 
the lake-region valley of Canada and the boundary. It has 
been easier for Metachlamydeae to move north and south 
in the western part of the continent, for the general movement 
has been from the south to the north; it has been easier for 
Monocotyledones to move south and north, in the eastern part 
—43 
