STATISTICS OF METASPERMAE. 723 
dones are prepondérant and the Archichlamydeae intermediate. 
In both the SE. and SW. elements the Metachlamydeae are 
preponderant and the Archichlamydeae intermediate. These 
facts are seen to be exactly in line with the rest that have been 
given. In the NW. element which is numerically the smallest 
of all the combination elements, the Archichlamydeae are pre- 
ponderant while the Monocotyledones and Metachlamydeae; 
for their respective numbers, contribute about equally to the 
element. This is probably to be attributed to two facts. 
First, the Siberian and the N. W. T. influence would be felt 
most strongly in the NW. element and this influence would 
consist principally of monocotyledonous and archichlamydeous 
forms. Second, the Monocotyledones of this influence would 
be generally more widely distributed in North America than 
the Archichlamydeae, so that they would be probably entered 
either in the NEW. or NSEW. elements. The Metach— 
lamydeae then through their endemic and north-bound char- 
acteristics and the Monocotyledones through their general and 
south or north-bound characteristics have either failed, on the 
one hand to make the N. W. rauge or, on the other have ranged 
beyond and are in the more general categories. The inter- 
mediate condition of the Archichlamydeae is then, after all, 
the cause of their preponderance in the NW. element. Ap- 
parently, too, if the existence of the diagonal tension, dis- 
cussed above, were borne out by further examination it would 
be possible for such a condition to appear in no other ele- 
ment than the NW. For in the NE. the Monocotyledones 
would have their greater ease of distribution to increase their 
preponderance while in the SE. and SW. the Metachlamy- 
deae would in varying ratios predominate. 
In general, then, the combination elements serve ‘to add to 
the weight of evidence in favor of considering the Metachlamy- 
deae, Archichlamydeae and Monocotyledones of different and 
more or less definite meaning as components. The two special 
cases are the NSW. and the NW. and an attempt, probably 
imperfect although, it is hoped, suggestive, has been made 
to show how in their case special topographical or geographical 
conditions have served to modify the more general biological 
conditions. 
Of the 1.174 species and varieties considered as indigenous 
to the Minnesota valley, 317 are of extracontinental range. 
This number is quite exclusive of the 130 species and varieties 
which have been introduced into the Minnesota valley during 
