INTRODUCTORY 3 
If plant production were not so important to the world, there 
would be little need of having domesticated animals. Our 
Fic. 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 
