FORTY YEARS OF .QENECOLOGY
231
wild. Under field conditions at Canberra, Australia, the time of flowering
was found to bear no very close relationship to the vernalization requirement of the different races, suggesting that in this locality other factors
- perhaps spring temperatures and photoperiod - may be determinative. He suggests that an interaction of vernalization temperature,
spring temperature and daylength may determine the developmental
period in the native areas of the races tested. Nevertheless, that genetical
variation in cold requirement does exist and that this can be related to
one important climatic parameter does suggest that the vernalization
response has been subjected to differential selection in various parts of
the natural range.
The role of photoperiodic responses in the adaptation of species of the
grasslands of North America to the climates encountered in various parts
of their range has been the subject of several studies in the last twenty
years. The work of Olmsted (1944a, b) on Bouteloua curtipendula remains one of the most satisfactory analyses. B. curtipendula has a wide
latitudinal range, extending from Mexico in the south to southem Saskatchewan in the north. Olmsted's study was based upon seed samples
derived from twelve sites spanning 17" of latitude. Comparisons were
made of growth and flowering periodicity under daylengths of 9, 13, 16
and 20 hours and under natural daylength at Chicago. A considerable
amount of variation appeared within the samples, but regularities in
their behaviour could be distinguished and related to provenance. The
periods from germination to f i s t flowering under the various photoTABLE V I I
Number of Days until first Flowering after Germination on 11
April 1942 of 12 Strains of Bouteloua curtipendula under
Different Photoperiods. [Data of Olmsted, 1944a.l
Photoperiod
Sourceofseed
LatitudeON
9 h
1 3 h
1 6 h
2 0 h
Nat.day
(Chicago)
North Dakota
Nebraska
Nebraska
'Nebraska
Kansas
Kansas
Oklahoma
Oklahoma
New Mexico
Arizona
Texas
Texas
-
73
69
-
95
95
-
123
123
109
40
-
-
109
109
-
109
123
109
39
37
-
-
95
123
-
73
-
123
-
81
-
123
-
464
42i
109
-
95
81
414
394
35*
323
294
294
55
81
95
-
-
-
95
81
-
32
-
-
-
-
55
73
95
81
109
109
123
109
109
231
wild. Under field conditions at Canberra, Australia, the time of flowering
was found to bear no very close relationship to the vernalization requirement of the different races, suggesting that in this locality other factors
- perhaps spring temperatures and photoperiod - may be determinative. He suggests that an interaction of vernalization temperature,
spring temperature and daylength may determine the developmental
period in the native areas of the races tested. Nevertheless, that genetical
variation in cold requirement does exist and that this can be related to
one important climatic parameter does suggest that the vernalization
response has been subjected to differential selection in various parts of
the natural range.
The role of photoperiodic responses in the adaptation of species of the
grasslands of North America to the climates encountered in various parts
of their range has been the subject of several studies in the last twenty
years. The work of Olmsted (1944a, b) on Bouteloua curtipendula remains one of the most satisfactory analyses. B. curtipendula has a wide
latitudinal range, extending from Mexico in the south to southem Saskatchewan in the north. Olmsted's study was based upon seed samples
derived from twelve sites spanning 17" of latitude. Comparisons were
made of growth and flowering periodicity under daylengths of 9, 13, 16
and 20 hours and under natural daylength at Chicago. A considerable
amount of variation appeared within the samples, but regularities in
their behaviour could be distinguished and related to provenance. The
periods from germination to f i s t flowering under the various photoTABLE V I I
Number of Days until first Flowering after Germination on 11
April 1942 of 12 Strains of Bouteloua curtipendula under
Different Photoperiods. [Data of Olmsted, 1944a.l
Photoperiod
Sourceofseed
LatitudeON
9 h
1 3 h
1 6 h
2 0 h
Nat.day
(Chicago)
North Dakota
Nebraska
Nebraska
'Nebraska
Kansas
Kansas
Oklahoma
Oklahoma
New Mexico
Arizona
Texas
Texas
-
73
69
-
95
95
-
123
123
109
40
-
-
109
109
-
109
123
109
39
37
-
-
95
123
-
73
-
123
-
81
-
123
-
464
42i
109
-
95
81
414
394
35*
323
294
294
55
81
95
-
-
-
95
81
-
32
-
-
-
-
55
73
95
81
109
109
123
109
109