Germination and Initial Growth of Eastern Cottonwood as Influenced by Moisture Stress, Temperature, and Storage

Germination energy of cottonwood seed decreased gradually as moisture stress increased from 0.0 to 10.0 atm; 15.0 atm inhibited germination except at 32 and 38 C. Temperature extremes of 15 and 38 C drastically reduced germination energy, and the reductive effect of 38 C was particularly marked after storage. Only 15-atm moisture stress or 15 C greatly reduced total germination. Germination under optimum conditions (27-32 C) was reduced from 90% to 69% by 12 months' storage. Little seedling growth took place at stresses above 5 atm and at temperatures of 15 and 38 C. Initial growth was related to seed size, which varied considerably with parent tree.