For a command-of-evidence question involving an experiment, identify the controlled comparisons required by the claim. Here, hold the grass line and second treatment constant while changing only the initial treatment. Repeat that comparison across both later conditions and both lines, then choose the answer that accurately describes the complete pattern rather than only one part of it.
Hints
- Hint 1
Hold other factors constant
Within each grass line, compare rows that have the same second treatment but different initial treatments.
- Hint 2
Check both later conditions
Determine the effect of the initial mild drought separately for plants that later experienced severe drought and plants that later received regular watering.
- Hint 3
Look for consistency and reversal
Ask whether the initial treatment has the same effect under both later conditions and whether the pattern occurs in both lines.
Step-by-step
- Step 1
Make controlled comparisons
To identify the effect of the initial treatment, compare plants from the same line that received the same second treatment but different initial treatments.
- Step 2
Examine the severe-drought results
During later severe drought, previously droughted plants gained more biomass than previously well-watered plants: 2.8 versus 2.0 grams in line R and 2.3 versus 1.7 grams in line S.
- Step 3
Examine the well-watered results
During later regular watering, previously droughted plants gained less biomass: 4.5 versus 5.0 grams in line R and 4.0 versus 4.4 grams in line S. Because the effect reverses depending on the second treatment, the data support a context-dependent drought memory in both lines.