PROPOSED EXPLORATIONS AND INVESTIGATIONS 249 



II. Problems. 



1. Relationship Betzvee7i Life of Northern America and Northern 

 Europe and Asia. — With regard to the relationship of the life of the 

 northern portion of the Old World to that of northern America there 

 exists the greatest diversity of opinion. Certain writers hold that 

 the life of each of the two great northern land masses shows enough 

 peculiarities of its own to warrant the recognition of a separate 

 Neardic region, and Paleardic region of primarj^ rank, each, there- 

 fore, coordinate with such biogeographic areas as the Australian 

 region, Ethiopian region, etc. Others equally competent to interpret 

 the facts regard the biota of the two areas as practically identical, 

 so that only when united to form a Holarctic region do they become 

 strictly comparable with the other primary geographic divisions of 

 the earth's life. In general European writers favor the former 

 view, while Americans unanimously support the latter. That such 

 radical difference of opinion can occur is mainly due to the fact that 

 each party bases its assumption on confessedly inadequate data, due 

 to the total lack of such definite information concerning the life of 

 Europe and Asia as is now available for northern America. As an 

 instance of the uncertainty which exists with regard to the actual 

 relationship of the life of the Paleardic and Neardic regions^ 

 the flowering plants, among the most carefully collected and 

 studied of organisms, maybe cited. In the latest edition of Gray's 

 Manual about 425 species are given as common to the northeastern 

 United States and the Paleardic region. Since the publication 

 of this work many of these have been critically studied and found 

 to be in reality aggregates of numerous closely related forms, no 

 one of which occurs on both sides of the Atlantic. The genera 

 Agrimonia, LinncBa, and A?itennaria are conspicuous examples. 

 As yet, however, no systematic general study of these species has 

 been undertaken, so that it is impossible to sb.y what conclusions in 

 regard to the relationship of the life of the Old World to that of 

 America may be drawn from the apparent similarity in this large 

 number of species, 



2. Life Areas of Northern Europe and Asia. — Equal divergence of 

 opinion exists on the question of the manner of distribution of life 

 within the two great land areas. The fact is generally admitted by 

 American writers that the life of the so-called Nearctic region is 

 arranged in zones, or belts of relative homogeneity, bounded by cer- 

 tain isothermal lines, and, like the isotherms, extending in a general 



