Effect of Climate and Soil upon Agriculture 21 
Region (6), surrounding Puget Sound, was a region of village life, the 
factor of control in this case being the fisheries. The houses of this 
region were built of wood from the abundant forest growth. 
Region number (7), the Great Basin, and number (3), the Rocky 
Mountain region, for the purpose of this discussion may be considered 
similar, in that the meagerness of natural products in both necessitated a 
thin and mobile population. 
There remains to mention region number (8), the Northern Woodland, 
in which the climatological conditions prevented aboriginal agriculture and 
necessitated a mobile population, moving about with the seasonal produc- 
tion of various resources which controlled their economic conditions. 
(By courtesy of Dr. M. R. Gilmore.) 
Compare the figure with Figs. 15, 22, 23 and 24. 
A study of Fig. 26 will serve to summarize the foregoing dis- 
cussion and at the same time orient it with respect to broad geo- 
graphic principles. .The curves drawn illustrate the relation which 
artificial factors bear to climate and plant growth. 
The increase of plant growth from desert to tropical regions is 
represented by an increase in the height of the shaded areas. 
(a) The first graph based upon the density of plant growth 
illustrates the ease with which man can gather plant food. 
(b) The second graph is, in a sense, the complement of the first. 
In regions where plant growth is sparse man is dependent upon 
animals to convert plant food into usable form. 
(c) With an increase in plant growth there is naturally an in- 
crease in the number of inimical plants. In arctic or desert 
regions weeds and harmful bacteria are relatively scarce and 
cause man little trouble. In tropical regions they are so numer- 
ous that even civilized man is at present unable economically to 
control them. 
(d-e) The majority of agricultural people have long been ac- 
climated to temperate conditions. Any attempt to change to a 
region where a normal body temperature of about 98.6° is not 
easily maintained results in serious physiological disturbances. 
These disturbances no doubt lower the vitality of colonists in 
tropical regions to a point where it has thus far been impossible 
for them to become independent of climate, and to do what, under 
III 
