Figure 7.

Sensitivity of P. tremula seedlings to GA₄ and GA₁. Hypocotyl length of 2.5-d-old seedlings are presented as an average of 40 seedlings ±se, except for the 10-μm treatment (30 ± se). Letters indicate statistically significant differences, according to Student's t test, in sensitivity to GA₄ as compared to GA₁; a, P < 0.001; b, P < 0.0001; and c, P < 0.01. At GA₄ concentrations greater than 100 nm and GA₁ concentrations higher than 1 μm the seedlings grew significantly taller than controls, P < 0.00001. The experiment was repeated once with P. tremuloides seedlings with very similar results.