THE PERMANENT REEGION. 
15" 
The effect the locust question is likely to have on the agriculture of 
the temporary region east of the Eocky Mountains, the boundaries of 
which we have found no reason for changing in any essential particular 
from what was given in map No. 1 of our first report, depends very 
largely upon the solution of the problem so far as it relates to the per- 
manent region. We shall therefore consider first this division of the 
subject. 
First. As to the Permanent Region. 
Since the publication of our first report the facts obtained have forced 
us to the conclusion that the boundaries of this region will have to be 
extended through more of the northern part of Nebraska and of Dakota 
than is included in our first map. The change we consider necessary is 
marked in the new map given in the present volume. The reader should 
bear in mind that by the term "permanent" we do not wish to convey 
the idea that the locusts are to be found breeding in all parts of this 
area each year, as we have stated in this and our former report that they 
are essentially migratory within this region, continuing in some sections 
for a year or two, and then changing to others, but that they are capable 
of continuing their race in any part of this region ; that it differs in this 
respect from the temporary region. In the latter the climatic conditions 
are such that they do not appear to be capable of continuing their race, 
the progeny of invading swarms deteriorating and finally fading out 
unless they return to their native habitats. That the boundaries be- 
tween these two regions cannot be marked with definite accuracy we 
admit, and hence in our former report mapped out an intermediate area 
to which we applied the term sub-permanent region, and, as will be seen 
by reference to the new map in this volume, we have still retained this 
region, though somewhat circumscribed. But the exact boundary is a 
matter of little importance practically ; the two regions as such are very 
easily distinguished from each other by marked characteristics. 
In the permanent region, which embraces the Eocky Mountain pla- 
teau and the bordering plains from the middle of Colorado northward, 
the rainfall is insufficient for agricultural purposes, and hence irrigation 
has to be resorted to ; in the temporary region this is unnecessary ; the 
plains and plateaus of the permanent region are to a large extent dis- 
tinguished by the presence of Artemesia, Chenopodiaceous plants, and 
what is usually termed "bunch-grass in short by all the characteris- 
tics of a drier climate. One other peculiarity which should not be over- 
looked appears to mark roughly the southern boundary of the permanent 
home of the Eocky Mountain locust, and that is the isothermal curve or 
line of the 50° of mean annual temperature, which also corresponds very 
nearly with the isotheral curve or line of summer temperature of 70°. 
But this applies only to that portion of the region which extends upon 
the plains east of the mountains. 
If any practical means of exterminating the locusts in this permanent 
region could be devised the whole locust problem could be solved, and 
