Part: IV. 
North American Phytogeographic Regions, Formations, Associatio 
Having presented in the foregoing part of this work a statement as to the affinities 
probable origin, past and present distribution of North American plants, it is now the 
to give a short account of the different phytogeographie zones, regions, formations and ass 
tions. Tbe consideration of the formations and associations of plant species will be made t 
two view points: the ecologic and the phyto-geographic. Beginning with the Arctie Zone, 
America, not exclusively from the floristie standpoint, but also from the ecologic, as well. 
endeavor will be to give a botanic description which will convey some adequate impressi 
the appearance and constitution of the flora, as it forms one of the component parts of 
landscape, setting off in artistie splendor our lakes, mountains, rivers, plains, deserts, hills > 
valleys. Necessarily, the description of the botanic regions must be short and very coneise, 
because of the strietures imposed upon the writer by the lack of space*) to present adequately 
such an important subject. # 
Chapter I. Arctic and Sub-Arctic Zones. 
1. Arctic Regions of Labrador, northern Mackenzie and 
e Arctic Shore. r 
The flora of Arctic America may be divided into three districts: 1. tha 
Greenland, which is almost exclusively Lapponian, having an extrei 
slight admixture of American, or Asiatic types, 2. that of east America fro 
the Mackenzie River to Baftin Bay, which shows a gradual transition ” 
3. west American district, west ofthe Mackenzie basin. These latter 5: 
will be considered alone in this work, because the transition in vegetation IFO 
the Greenland district to that of east America is comparatively very 4 
Tundra conditions prevail over the greater part of this vast territory, W" 
the ground remains perpetually frozen to an unknown depth, thawing - 
only a foot or so on the surface during the summer. A large number 
plants grow in the thin coat of soil resting upon perpetual frost. Wild 
able to pollinate the flowers abound and mosquitoes swarm by the m 
*) Bemerkung der Herausgeber: Zwingende Rücksichten ließen es notwendig ersC 
daß die von Prof. Dr. HARSHBERGER für Part IV eingesendeten Nachträge, besonders die = 
lichen Pflanzenlisten, in diesem “Survey” nur sehr verkürzt abgedruckt wurden. > 
