This research compared results from germination and growth when the ex
periment duration was chronologically set or based on degree-days, See
ds of smooth brome (Bromus inermis Leyss.), plains rough fescue (Festu
ca altaica Trin, subsp, hallii (Vasey) Harms), prairie coneflower (Rat
ibida columnifera (Nutt.) Woot. and Standl.), and silver sagebruh (Art
emisia cana Pursh.) cvere germinated at 5, 10, 15, 20, and 25 degrees
C for 28 days or 400 degree-days (Base temperature = 0 degrees C). Roo
t and shoot weights of seedlings of these species were compared at 5,
10, 15, 20, 25 and 30 degrees C after growing them 20 days or 200 degr
ee-days, With the exception of prairie coneflower, optimal temperature
s for germination were 2 to 4 degrees C lon er when incubated 400 degr
ee-days compared to 28 days, Total germination for prairie coneflower
was not significantly different (P =0.454) at 28 days or 400 degree-da
ys, Interacting effects of the duration of experiments and temperature
significantly (P less than or equal to 0.001) influenced root and sho
ot weight of all species, Except for shoot weight of smooth brome, pre
dicted optimum temperatures for root and shoot growth were 7 to 21 deg
rees C lower at 200 degree-days than 20 days. These experiments illust
rate that results from germination and growth studies can vary substan
tially depending on whether chronological time or degree-days are used
as the end point, Thus, ecological interpretations or management reco
mmendations can be quite different, Degree-days may be more meaningful
than chronological units for germination and growth studies because t
hey integrate time and temperature, The use of degree-days as an end p
oint for experiments rather than chronological time deserves further c
onsideration by researchers.