424 TEXTBOOK OF BOTANY 



the plants of the forest are needed, we still use many of the native wild 

 species. The origin of these wild species will be considered in a later 

 chapter. Many of the plants we use, and especially our crop plants, have 

 been obtained from wild species by repeated selection of more desirable 

 variations, and in recent times by selection accompanied by controlled 

 pollination. Even forest trees are now being selected and artificially 

 pollinated to obtain varieties with certain desired qualities. 



When man transfers plants from the wild state and provides artificial 

 environments favorable to their growth and propagation, he observes 

 many of the variations that naturally occur in them and eventually selects 

 and maintains certain of the new varieties. These cultivated varieties are 

 often referred to as agronomic, horticultural, and garden varieties, or 

 briefly as domesticated plants. 



Many domesticated plants are unable to survive in the natural condi- 

 tions that prevail over most of the area in which they are cultivated. 

 Domesticated annuals, for instance, may perish because their seeds do 

 not survive from one growing season to the next unless they are preserved 

 in artificial conditions. Some domesticated varieties, such as special 

 hybrids of corn, are reobtained each season only by carefully controlled 

 pollination. On the other hand some domesticated plants, through seed 

 dispersal, may become distributed and continue to persist as weeds in 

 fields and along roadsides, but they usually do not survive in areas occu- 

 pied by native plant communities. 



A heritage from prehistoric man. Nearly all of our more important 

 species of cultivated plants were domesticated by prehistoric man. Nu- 

 merous new varieties have been obtained from these domesticated plants 

 within historic times, but the domestication of additional wild species 

 has been limited largely to plants chosen for decorative purposes or for 

 their fruits and their forage value. 



On the basis of our present knowledge of plants, we may, with reason- 

 able certainty, enumerate the major steps by which prehistoric man 

 secured domesticated plants. First, there was a recognition of certain 

 valuable parts or properties in the wild ancestors. For a time these parts 

 were collected from the plants wherever they were found in a wild state. 

 Later particular species were intentionally cultivated. Variations in the 

 heredity of the cultivated individuals continued to occur by the same 

 process that brings them about in plants in the wild state. Under the 

 conditions of cultivation, seeds or vegetative propagules of some of the 

 variants were either consciously or unconsciously selected and planted 



