286 THE AMERICAN NATURALIST. | [Vor. XXXIV. 
over, if this diversity exists, it is of great value to the ranch- 
man or orchardist to be made aware of it, since he will not 
then waste time and money by setting out plants which cannot 
be expected to succeed. 
As a matter of fact, such problems as these have already 
been largely solved in the cultivated areas, by the experience 
—often tedious and expensive — of the residents. But they 
have not been solved for the areas which may yet be brought 
under cultivation, nor are the facts sufficiently accessible to 
residents in other states who expect to locate in the arid west. 
Yet again, even those residents who are satisfied with what their 
own locality will produce, are usually not acquainted with the 
possibilities of other districts, possibilities which affect them 
in so far as they affect the markets. 
Last spring the writer had the pleasure of meeting Dr. 
Merriam at Washington, and at his suggestion made for him 
alist of the commoner trees and shrubs of the Mesilla Valley. 
Dr. Merriam, glancing over this, at once said : ** With possibly 
one or two exceptions, these are a// Lower Sonoran types." 
My investigations in the Salt River Valley have convinced me 
of the justice of this statement, and it may be said at once 
that, so far as the native flora is concerned, the Mesilla and 
Salt River Valleys may very well be placed in the same zone. 
The illustrative data given further on suggest more precisely 
the actual condition of affairs. Many of the plants which are 
abundant and conspicuous in the landscape are entirely the 
same, while others are so similar that they may be held to 
indicate rather the fact that we are three hundred and odd 
miles to the west of the New Mexico Valley than in a different 
life zone. In the list of insects common to the two valleys, 
also, we find many of the characteristic Mesilla Valley types, 
described as new from thence in recent years. The absolute 
differences, discussed under headings 3 to 5, are important 
in their way, and doubtless will be emphasized by further 
research; but it is at least questionable whether they indicate 
a different life zone, or, rather, whether they would fice 
one if no other facts supported the division. 
Turning now to the cultivated products, the conditions are 
