226 INTRODUCTION TO PLANT GEOGRAPHY 



white race nowadays. Their areas of origin are doubtful but were 

 evidently diverse as regards the different forms, some of which 

 appear to have been cultivated for at least 6,000 years. Nevertheless 

 the predominance of Wheats is relatively modern, other cereals, or 

 mixtures comprising maslin, having been previously more widely 

 used for bread. Wheats were probably developed by selection from 

 weedy types and hybridization with other Grasses, but are still being 

 improved today. They are grown under a wide variety of climatic 

 conditions, including some tropical ones (in winter), and, like 

 polymorphic weeds, are the more widespread because of their 

 diversity. Nevertheless the general distribution of Wheats is mainly 

 temperate, as indicated in Fig. 67. 



Less widespread and important are Barley {Hordeum milgare s.l.), 

 Oats {Avena sativa and other species), and Rye {Secale cereale), 

 though the first of these is probably the oldest of our major cereals 

 and possibly of all currently cultivated plants. It was widespread 

 already in Neolithic times and was used for bread even before Wheat. 

 Oats probably had a long history as a weed in fields of primitive 

 Wheat before becoming a crop in its own right, while Rye, which 

 was unknown before the Iron Age but is now the world's second 

 most important bread crop, apparently originated as a grain-field 

 weed in Asia Minor. It can be grown on poorer soils than other 

 cereals. Owing to its greater winter hardiness and ability also to 

 mature grain under less generally favourable conditions than the 

 other cereals mentioned, Rye tends to be cultivated chiefly in 

 mountainous regions and about the northern limit of the Wheat 

 belt, being important chiefly in the cool-temperate parts of the 

 northern hemisphere — cf. Fig. 68. However, Barley is able to 

 mature in a shorter summer than the other cereals, and so is the 

 only one which the writer has seen being grown successfully for 

 grain north of the 70th parallel of latitude in Norway. 



Maize [Zea mays) is the largest of the cereals. According to that 

 foremost student of its history. Professor Paul C. Mangelsdorf of 

 Harvard University {in litt. 1957), ' No wild ancestor is known with 

 certainty, but fossil pollen believed to be that of wild Maize has 

 been found at a depth of more than seventy meters below the present 

 site of Mexico City. Other evidence points to cultivated forms of 

 Maize originating on the eastern slopes of the Andes in South 

 America. Maize cultivation goes far back in prehistoric times. 

 Grains found in burial sites in Peru already represent several different 

 varieties, indicating that the plant had been grown for many centuries 



