742 METASPERMAE OF THE MINNESOTA VALLEY. 
ceding chapter, where the original presence of palms 
and allied forms was. discussed. On the other hand, 
the Metachlamydeze with their 1.8 per cent. of trees and 
7.1 percent. of shrubs have as yet failed to develop many 
shrubby or arboreal plants in this latitude. The antiquity and 
lower organisation of the Monocotyledones are therefore seen 
to have been reflected in the physiognomy of the valley to-day 
in a manner similar to that in which the recentness and higher 
organisation of the Metachlamydeze have been reflected. The 
absence of monocotyledonous trees and shrubs is due to their 
having been obliterated ages ago by the stronger archichlamy- 
deous forms, together with the geological progression of climatic 
and topographical changes. The absence of the metachlamy- 
deous trees and shrubs, compared with the abundance of the 
Archichlamydez,is doubtless owing to entirely different causes. 
Not obliteration but failure to reach the valley is the explana- 
tion of their absence. Paleontological remains do not indicate 
that metachlamydeous trees or shrubs were ever before so 
abundant in the Minnesota valley as they are to-day. Thesame 
evidence shows that in the Cretaceous and Tertiary periods 
there were palms in the valley. Thus by direct evidence is 
corroborated what might a priori be derived from the study of 
modern distribution. Together with the predominant herbace- 
ousness of the Monocotyledones must be read their antiquity 
and their preponderantly extra and intra-continental width of 
range. Together with the only less predominant herbaceous- 
ness of the Metachlamydez must be read their recentness and 
their preponderantly endemic and limited range. Thus the 
character of the other taxonomic group may be stated in 
terms as follows: 
The Archichlamydez, forming 86.7 per cent. of the arboreal 
element and 72.1 per cent of the shrubby element have on the 
one hand had sufficient time to develop their habit and to reach 
the Minnesota valley, while on the other hand they are not to 
such an extent a lower group, nor so ancient that they have 
been erased from the distinctively extratropical regions. 
From both sides they have been favored in the development of 
arboreal characters, and for ages will doubtless maintain them- 
selves in extratropical regions as the characteristic trees and 
shrubs, although ultimately, the logic of history would seem 
to destine them for extinction under the attack of arborescent 
Senecios, Helianthi or Solidagos, or of other composite or composite- 
like forms that had attained the arboreal habit. 
