Further evidence is presented in support of the hypothesis that a morphogenetic factor, or factors, is present in older primordia which is transmitted to younger primordia to influence the latter to develop as leaves rather than shoots. P3primordia, undetermined at the time of excision, are expressed asleavesat a level of 60.0% when explanted to a simple, defined medium containing, in addition, homogenate of determined P12primordia and at a level of 70.0% when grown on medium containing homogenate of P13primordia. By contrast, undetermined whole P3's are expressed asshootsapproximately 70.0% of the time when excised and explanted to: (1) a homogenate-free medium, or (2) medium containing homogenate of undetermined P3's. Of greater significance is the observation that undetermined P3's are expressed asshootsat approximately the same level when excised and explanted to medium containing homogenate of determined P14primordia. The relevance of these phenomena to a physiological aging process is briefly discussed.