284 PLANT GROWTH SUBSTANCES 



kind of plant organ, that such morphogenetic substances are syntP,esized 

 only in certain cells, tissues, or organs, and/or that they are produced at 

 specified stages of development. The results we have obtained are in 

 disagreement with such concepts. On the contrary our findings suggest 

 that both organ formation and subsequent development are brought 

 about by quantitative changes in amounts and interactions between 

 nutrients and growth factors which are essential for growth of all cells, 

 so that the pattern of development is determined by the relative supplies, 

 through synthesis, transport, and accumulation of these materials at 

 particular loci. On this basis, the morphogenetic capacities of a given 

 cell or tissue are limited not only by its genetical potentialities for 

 syntheses but more often by its morphological environment, that is, 

 by its particular position in the structurally complex plant body. This 

 concept demands that normal growth of cells must lead to a unified 

 general pattern of development in all plants of comparable genetic 

 constitution, but it permits infinite variation in details. 



As a working hypothesis, it lacks the conciseness of concepts invoking 

 the participation of a specific substance for each step in morphogenesis, 

 but it offers equal opportunities for the separation of individual growth 

 factors. In addition, it provides an over-all plan for both physiological 

 and morphological experimentation on correlation phenomena, which, 

 we believe, must control structural organization at all levels in the 

 development of plants. 



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