372 BOTANICAL GAZETTE [NOVEMBER 
greater uniformity of detail in the two charts. The numerical data 
indicate, furthermore, that it would be quite impossible to make 
one chart more like the other by choosing other values through 
which to pass the isoclimatic lines. 
The most striking difference between these charts (figs. 1 and 2) 
is seen in the basin and Pacific regions. Nowhere on the Pacific 
coast does the efficiency index fall below 400, while the northern 
half of this coast characteristically exhibits direct indices below 
4000, Tatoosh Island, Washington, having a direct index as low as 
3054. Thus it has been impossible to draw the lines on the chart 
of direct summations so as to bring the northern area with indices 
above 4000 (from Great Salt Lake to the Columbia River) into 
conjunction with the southern area having the same sort of indices 
(California, Arizona, etc.). On the efficiency chart these two areas 
become joined, however. Other less striking quantitative differ- 
ences are clearly enough indicated, and this sort of inspection 
establishes the fact that the ratio of the direct summation index to 
that of efficiency can by no means be regarded as constant for the 
whole country. It is of course to be remembered that the hypso- 
metric map has been called into requisition in the placing of our 
isoclimatic lines, the stations for which data are available being far 
too few and too far apart to give the detailed information which 
such charts require. N evertheless, it seems perfectly clear that 
while the isoclimatic lines may really have other positions than the 
ones here assigned them (it is safe to suppose that almost every 
centimeter of these lines would be displaced to some extent if more 
data were at hand), yet the discrepancies between the two charts 
are not primarily to be related either to lack of data or to careless 
or inefficient interpretation of the information at hand. 
Our arithmetical treatment of this question of the value of the 
ratio of the direct index to the index of efficiency brings out the 
fact that this ratio varies, for the stations employed, from 7-49 
(Tatoosh Island, Washington) to 10.44 (San Luis Obispo, Cali- 
fornia) or 10.33 (Anniston, Alabama). As has been mentioned, 
the values of these ratios are presented in fig. 3, where lines at 
shown for the ratio values 8.00, 9.00, 9.50, and 10.00. This 
chart brings out the geographic distribution of these various values. 


