CHAPTER 20 



Organization 



Underlying the various phenomena of morphogenesis that have here been 

 discussed stands a single basic problem: how a mass of living stuff is 

 organized into a system, so well termed an organism. Organization is evi- 

 dent in various ways but most vividly in the development of form in 

 living things. Form is not simply a trait to be described and classified. 

 It is also the visible expression of a self-regulatory equilibrium which 

 tends to be attained in development, maintained during life, and restored 

 when disturbed. Every individual has a specific equilibrium of this sort, 

 a morphogenetic norm, so to speak, to which it tends to conform. This is 

 the unifying factor that gives continuity to an organism. It is a pattern 

 for development in which every part, in its growth and activity, is related 

 to all the others and by which the fate of each is determined by its posi- 

 tion in the organized whole. 



The manifestations of a given norm are various. It is not constant in 

 expression but may change, in a precise and regular fashion, from embryo 

 to maturity. It may produce very different results under different en- 

 vironmental conditions. Its basis is established in the genetic constitu- 

 tion of the individual. The nature of this norm, how it is modified in ex- 

 pression by factors inside and outside the organism, and how develop- 

 ment is regulated in conformity to it are the basic questions with which 

 the science of morphogenesis must deal. 



To attack this problem hopefully one should break it down, if possible, 

 into simpler components. These have already been discussed in earlier 

 pages, but it will be useful here to bring them briefly together into focus 

 on the main problem. 



One of these components is polarity. All plants, at least at certain 

 stages, are organized around an axis which provides a basis along which 

 development takes place and in relation to which the lateral organs are 

 formed. The two poles of this axis (save in rare cases) are unlike. The 

 axis may be vertical or horizontal, and if lateral axes arise from it, these 

 often have specific orientations, so that the plant body is really a pattern 

 of polarities. In many cases transverse as well as longitudinal ones may 



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