18 BULLETIN 307^ U. S. DEPAETMEXT OF AGRICULTURE. 
but little attention has been given to seed selection, most of the 
so-called varieties vary widely within themselves, and estabhshed 
types are few. In varietal tests containmg these varying types any 
small differences which may appear are obviously of little importance. 
In varietal tests in which seed is assembled from different locaHties 
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 un\\dse to introduce 
seed from a distance for general planting, even if the introduced seed 
has proved to be of superior value where gTo^vii. 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 strikuigly 
unadapted, this practice is obviously unfah 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- 
mg the operation and effect of these so-called accUmatization and 
adaptation factors. Some varieties do well m cert am locahties or 
under certain conditions, but seem unable to respond to changed 
conditions. Other varieties are more adaptable and perform weU 
under widely different conditions. To assume that a variety is 
best for a locahty because it has had an opportunity to become 
acchmated may be as false a conclusion as to assume that a variety 
will do well m one locahty because it has done so m some other 
locahty. 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 bruigmg 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 aU the tests, is given m 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 outstandmg of these have 
been White Austrahan, Martens White Dent, and U. S. Selection 133. 
Two of these have been growm under Plains conditions for a num- 
