The normal development of the higher plant occurs only in light (photomorphogenesis). The effect of light is due to intracellular development of a morphogenetically active effector molecule (Pfr, a chromoprotein). The point in question is, by which pathways the homeostasis of development (the course of development directed by endogenic factors) and the environmental factor "light" may act together in photomorphogenesis in order to accomplish the normal development of plants. Physiological and molecular analysis of photomorphogenesis is to contribute basically to the problem of surveying the pathways of gens and environmental influences in determining the characteristics of higher organisms, man included. The logical order of the phenomena is shown to have the precedence of an attempt for molecular analysis of photomorphogenesis. A result of the logical order is the insight that all the phenomena induced by Pfr present the spatial and temporal pattern of "primary differentiation". This primary differentiation (= formation of the specific competence) does not depend on light (developmental homeostasis). The photomorphogenesis (= development through the presence of Pfr of the pattern due to the primary differentiation), in accordance with the present knowledge is to be attributed to differential enzymatic induction and repression. This opinion is confirmed by examples. The correlation between the enzymatic activity and the structure (form, shape) still remains an unsolved problem.