The development of crown gall tumors on decapitated pea seedlings grown in vitro is evaluated in terms of the mean weight of excised tumors. Reproducible quantitative results are obtained when mean weights of tumors are adjusted for the growth of lateral shoots. The regression line for tumor weight on the length of lateral shoots suggests that the growth of tumors and shoots is competitive. Optimal tumor formation occurs when seedlings are inoculated either immediately or within a few hours after decapitation of the seedlings. Wound healing after decapitation is not accompanied by the appearance of cells in stages of active division. Dividing cells are not observed in tissues below decapitation sites unless seedlings are inoculated with the crown gall bacterium. In darkness, large tumors develop within 2 weeks on inoculated seedlings kept at 24 °C. However, although normal growth continues, tumor formation is almost completely inhibited at 15 °C. When inoculated seedlings are held at 24 °C and 15 °C for alternate periods of varying duration, the adjusted tumor weight decreases as the duration of the period at the lower temperature increases. However, tumor size is not determined simply by the time interval during which plants are exposed to the inhibiting temperature, but also by the order of exposure to the two temperatures.
Physiological Comparisons of Pith Callus With Crown-Gall and Genetic Tumors of Nicotiana glauca, N. langsdorffii, and N. glauca-langsdorffii Grown in Vitro. II. Nutritional Physiology