68 GEOGRAPHICAL DISTRIBUTION 
old world in pre-historic time. It has been found among the re- 
mains of the lake-dwellings of the stone period, probably arriving 
there through Russia and Austria from China and Japan. The 
specific name is inappropriate. Sorghum vulgare, dourra or 
Kaffir-corn, and Sorghum saccharatum, Sweet-sorghum, are (with 
maize) exceptional among the cultivated grains in having been 
dispersed eastward ; they are largely cultivated in tropical Africa 
and are probably native there, having spread from Egypt into 
Arabia, India, and China. Panicum miliaceum was cultivated in 
pre-historic time in Southern Europe, Egypt, and Asia; it grows 
wild south of the Caucasus. Edeustne coracana is largely cultivated 
in Southern Asia and the Malay Archipelago, where it is probably 
native, 
For further information on this subject, refer to A. de Candolle’s 
Origin of Cultivated Plants. 
The geographical distribution of the cereals at the present day 
falls broadly into three zones or mighty girdles around the earth— 
a tropical, a north temperate and a south temperate. They are by 
no means sharply defined from each other, especially in the northern 
hemisphere, where a commixture of the tropical and north temper- 
ate zones extends over several degrees of latitude. 
The broadest zone is that of the tropical grains—maize, rice and 
millets. Maize is distributed over 90° of latitude—45° on each side 
of the equator, including all the United States, Central America, 
and South America except the extreme southern part of the 
peninsula, the whole of the continent of Africa, the southern por- 
tion of Eurasia, all Malaysia, and Oceania. The rice belt is not so 
broad, as although in Europe its northern climatal limit coincides 
almost with that of maize, it is 10° nearer the equator on the 
continents of North America and Asia, and its southern boundary 
is similarly curtailed. Millets, most generally cultivated in Africa 
and Asia, have as wide a range of temperature as maize. 
The northern zone of temperate grains—wheat, barley, oats 
and rye—has a breadth of go” of latitude in the old world, but 
scarcely 30° on the American continent, because the extreme 
continental character of the climate prevents cultivation far north- 
ward. The polar limit is erratic. On the humid Pacific slope of 
North America it is probably near the 55th parallel, somewhat 
higher on the eastern side of the Rockies (which deprive the S.W. 
winds of their excessive moisture), falling gradually to 50° as we 
cross the continent to the Atlantic. In Western Europe it recedes 
to the 7oth parallel (the effect of the warm Gulf-Stream), but 
excludes Iceland; in Western Siberia it approaches 60°, and in 
Eastern Asia falls to about 50°. The equatorial limit of the north- 
ern zone varies with the elevation of the earth’s surface ; in India it 
passes to the south of the Tropic of Cancer onthe Deccan plateau ; 
on the plains of the Western Continent it is a few degrees north of 
that line. 
