18 BULLETIN 30*7, U. S. DEPABTMENT OF AGRICULTURE. 



but little attention has been given to seed selection, most of the 

 so-called varieties vary widely within themselves, and established 

 types are few. In varietal tests containing these varying types any 

 small differences which may appear are obviously of little importance. 



In varietal tests in which seed is assembled from different localities 

 those varieties usually give the best results which have been grown 

 for some time under conditions similar to those where the test is 

 made. Such varieties are said to be acclimated or to have become 

 adjusted to the conditions where grown. Much emphasis has been 

 laid on the importance of this factor. The usual recommendation is 

 that if locally grown seed can be secured it is unwise to introduce 

 seed from a distance for general planting, even if the introduced seed 

 has proved to be of superior value where grown. While this recom- 

 mendation seems to be justified by the large number of cases in which 

 the locally grown seed has proved superior, it has in some cases been 

 overemphasized by comparing averages rather than the performances 

 of individual varieties. Since wide differences usually occur among 

 introduced varieties and: the average is lowered by those strikingly 

 unadapted, this practice is obviously unfair to the best varieties. 



While natural selection is said to operate to adjust varieties to the 

 conditions where grown, there is very little exact knowledge regard- 

 ing the operation and effect of these so-called acclimatization and 

 adaptation factors. Some varieties do well hi certain localities or 

 under certain conditions, but seem unable to respond to changed 

 conditions. Other varieties are more adaptable and perform, well 

 under widely different conditions. To assume that a variety is 

 best for a locality because it has had an opportunity to become 

 acclimated may be as false a conclusion as to assume that a variety 

 will do well in one locality because it has done so in some other 

 locality. There seems at present to be no rule by which the per- 

 formance or relative adaptation of different varieties to different con- 

 ditions can be determined except by bringing them together in 

 comparative tests. 



In the summaries of tables previously given, the varieties are 

 divided into three classes, according to whether the comparative 

 yields are good, average, or poor. The standing of all varieties 

 according to this classification, from all the tests, is given in Table 

 VII. 



Certain varieties have given good results in nearly all tests. Their 

 yields have varied widely as conditions were favorable or unfavor- 

 able, but their production as compared with that of other varieties 

 has remained uniformly good. The most outstanding of these have 

 been White Australian, Martens White Dent, and U. S. Selection 133. 

 Two of these have been grown under Plains conditions for a num- 



