234 INTRODUCTION TO PLANT GEOGRAPHY 



plants, often virtually as extensive as climatic possibilities allow, but 

 by special breeding and cultivation techniques Man is always 

 endeavouring to extend the potential areas into new regions. This 

 is notably true in the case of Wheat, the northern limit of which 

 has been pushed farther and farther towards the Arctic in recent 

 decades. It is chiefly with the currently attained areas of the most 

 important herbaceous crops (as opposed to ' woody ' ones, treated 

 afterwards) that the present section will be concerned. And whereas 

 the major vegetational belts and hence natural plant distributions 

 may to some extent have conditioned human migration in the past, 

 it is largely the crop-growing potentialities of different regions that 

 determine the density of human population today. This we shall 

 see in the next chapter, though with the modern ease and efficiency 

 of transport, particularly, this general conclusion tends to become 

 less and less applicable in some areas of intense industrial or mining 

 productivity. 



We will now indicate briefly on a world-wide basis the significance 

 and chief areas of cultivation of some of the more important and 

 familiar herbaceous crops ; ornamental ' flowers ' are apt to be even 

 more widespread owing to the special care, often including develop- 

 ment under greenhouse or other highly artificial conditions, that is 

 lavished upon them. The chosen examples will be treated under 

 eight main headings. 



(i) Grains — The principal grains occupy about one-half of the 

 world's croplands and of them Rice {Oryza sativa) is probably the 

 most generally important, being ' an indispensable food of over half 

 the population of the world '. It replaces the other cereals as the 

 stafl^ of life in many tropical and subtropical countries, and in several 

 of the most densely populated of these its cultivation is the chief 

 agricultural industry. Although 95 per cent, of the Rice cultivation 

 of the world is in the Orient, where the crop presumably had its 

 origin far back in antiquity, Rice is now cultivated practically 

 wherever in the tropics its usual needs of abundant moisture can 

 be economically satisfied, its distribution aflording a good example 

 of that of a warm-climate crop {see Fig. 66). For the many types 

 of lowland Rice, which have to be flooded during part of their 

 development, are the ones growai almost exclusively ; relatively 

 unimportant is ' upland ' or ' hill ' Rice, which can be cultivated 

 in drier situations much like those favoured by other cereals. 



Wheats {Triticum vulgar e and other species) constitute the chief 

 cereals of temperate regions and the ones most important to the 



