Effect of Climate and Soil upon Agriculture 107 
ACRES 
PER PERSON 
Ea ee 
Ly) 
GREAT PLAINS Alles EASTERN UNITED STATES 
Fic. 18. Land per person increases rapidly near the line of critical mois- 
ture. (See Index to Graph, Fig. 15.) 
ACRES. 
PER PERSON 
Gaara 
Fic. 19. Land per person increases rapidly near the line of critical tem- 
. perature. (See Index to Graph, Fig. 15.) 
ACRES 
PER PERSON 
N.RUSSIA Miles. S.RUSSIA 
ee, 
° 70o 
Fic, 20. Land per person from northern to southern Russia. (See Index 
to Graph, Fig. 16.) 
107 
