the conditions remain within a critical range, one kind of ecotype 

 will prevail. But if the conditions change beyond this range, then 

 it can be expected that a sorting of biotypes will lead to an in- 

 crease in the better-adapted kinds and a decrease or disappear- 

 ance of others, resulting in time in a new ecotype, and conse- 

 quently in increased capacity to grow under changed conditions. 



New biotypes apparently can readily form when plants are 

 grown in a new habitat for a few generations. Strains of forage 

 plants, for example, from a northern latitude, when grown for two 

 or three generations in more southern latitudes, show increased 

 susceptibility to frost and decreased production of green forage 

 when grown again in the north, ^^s Therefore, in hastening the 

 production of seed of a new strain by growing it in a more favor- 

 able region, the length of time in this region should be limited to 

 one or two generations at the most, so natural selection of new 

 biotypes will not modify the characteristics of the strain. 



Hybridization also produces new types that may be more effi- 

 cient than the parents in utilizing the resources of the environ- 

 ment. Habitat preferences are inherited in substantially the same 

 fashion as any other character, so many hybrids are unlikely to 



Figure 1-10. Genetic diversity in height, leafiness, date of 

 maturity, and seed production is shown in strains of Canada 

 wildrye growing in an observational nursery, Pullman, 

 Washington. (U.S.D.A. Soil Conservation Service.) 



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