Effect of Climate and Soil upon Agriculture 15 
coniferous and broad-leaved forests, the boundaries between tem- 
perate and semi-desert grass lands, and the boundaries between 
northern coniferous forests and semi-desert grass lands. 
10 Cr/ticg/ Cold 
@Criticol 7ea7- 
\CrittCa/ Fratnfe// 
Index To Grapghy 
Fic. 16. Critical agricultural lines in Europe. 
The natural factors which give such striking characteristics 
to the distribution of native vegetation give equally striking char- 
acteristics to the distribution of people and the organization of 
farm business. A study of graphs based upon the area of land 
per person in the United States (Figs. 18 and 19), Russia (Fig. 
20), and China (Fig. 21) will serve as a general index to the 
tate at which the organization of farm business changes near 
105 
