INTRODUCTORY 



8 



If plant production were not so important to the world, there 

 would l>e little need of having domesticated animals. Our 



FIG. 2. Dense vegetation as seen in a tropical forest 



During the relatively dry season, water may cease flowing in the stream bed 

 here shown, but even then almost all available space is occupied by plants. Dur- 

 ing wet seasons in such regions plants often grow upon one another in quantities 

 that break down the supporting stems 



domesticated plants have been derived from wild ancestors. 

 Many of these have been improved, until now their prod- 

 ucts are of much better quality or quantity than in their wild 



