PLANTS IN ARID REGIONS—SPALDING. 455 
for desert planting is being determined. From the great number of 
plants successfully cultivated there seems, at first sight, to be suf- 
ficient justification for the reiterated assertion that anything will 
grow here if you only give it water enough, but closer attention to 
the actual facts of the case makes it evident that this statement is 
true only in part, and that there are many plants that will grow only 
indifferently or not at all under the atmospheric conditions which 
prevail here, especially in the summer time. To give a few ex- 
amples, geraniums, the universal easily raised plants of moister 
regions, are very uncertain, some varieties accommodating them- 
selves fairly well to the desert air, while others fail altogether. 
Cannas and gladiol, which grow side by side in the east, part com- 
pany here, the former making a good growth in Arizona Paeiens the 
latter eee altogether. Tina who have handled roses for a period 
of years have learned what varieties may be expected to do well in 
the dry air of the desert, and what ones may be counted out, and so 
on through a long list of plants which, by knowledge gained in the 
costly school of experience, are coming to be depended on, or are being 
rejected one after another, as they are found to be unsuited to the 
environment into which they have been brought. Thus, in a purely 
empirical way, it has been found that many plants successfully cul- 
tivated in regions of greater atmospheric humidity make an entirely 
normal growth in the desert, if their roots are well supplied with 
water, but that others, however well cared for in this respect, either 
fail completely, or come short of making a healthy growth, and that 
this is especially true in the summer months when desert conditions 
are most pronounced. 
With the accumulation of such facts the more evident does it 
become that a very complicated problem is here presented. Why is 
it that one plant, properly watered, does well in the desert, while 
another, though treated in the same way, makes a poor growth or 
fails altogether? At first thought it would seem as though there 
must be a difference in the capacity of the root systems of the two 
plants for absorption, and that this may be a sufficient explanation 
of their different behavior; but it is evident on consideration, that 
with precisely the same capacity for root absorption, a plant in 
which transpiration is successfully regulated may thrive in an 
atmosphere in which one subject to excessive transpiration will 
perish. The most elaborate experiments and the most exact deter- 
minations of rate of absorption—assuming that such determinations 
are possible—would be very likely to throw no light on the problem. 
Comparisons of the transpiration rate of the plants in question 
appear more promising, but the same difficulty arises in an attempt 
to pursue the investigation along this line, for there is no reason to 
suppose that two plants of widely different rates of transpiration 
45745°—sm 1909——3@ 
