558 PLANT GROWTH AND PLANT COMMUNITIES 



explained in classical chemical and physical terms. For respiration 

 follows the second law of thermodynamics: it results in an increase in 

 entropy. But the growth process is not a process of dissimilation; it is 

 one of assimilation. I believe that this is the main reason why the 

 biochemical approach has scored such spectacular successes in advanc- 

 ing our understanding of respiration, whereas it has failed, equally 

 spectacularly, to help us in understanding the growth process, as was 

 so clearly demonstrated in the paper by Dr. Bonner. The preoccupation 

 of so many modern biologists with biochemistry and biophysics, which 

 have shown that partial processes in the organism follow the laws of 

 the inanimate world, has often closed their eyes to the much more 

 basic aspects of biology: namely, those in which the processes do not 

 follow the laws of thermodynamics. This, I submit, is the real content 

 of biology. Similarly, the assimilating aspect of growth, since it is op- 

 posed to the second law of thermodynamics, is the more interesting 

 problem, because one does not deal with already established facts and 

 also because it is such a basic problem of life. 



We assume that the assimilatory processes of growth are tied in 

 energetically with respiration. When we calculate the over-all energy 

 balance, we find that, on the whole, growth is attended by an increase 

 in entropy. But the major problem in connection with organic synthe- 

 sis in relationship to growth is that the direction of the formation of 

 the organic constituents of the cell is fixed and is contrary to what 

 would be expected theoretically. For thermodynamically we would ex- 

 pect an increase in randomness to result from chemical transformations 

 in the growing and living organism. The lack of randomness, or de- 

 crease in entropy, that actually occurs can only be conceived as due 

 to directive forces, in the nature of polarities. It is not sufficiently 

 stressed that basically most of these processes of synthesis and growth 

 are irreversible. And irreversibility is another aspect of polarity. It 

 causes proteins and other substances essential for cell growth to form 

 instead of to disappear. This excess of synthesis over disintegration re- 

 quires directive forces. 



We encounter polar phenomena everywhere in living organisms, 

 and in all cases they are equally poorly understood in terms of physical 

 and chemical counterparts. Polarity, for instance, is the process that 

 makes salts accumulate inside cells. We know something about the 

 sources of energy for this salt accumulation, and even have models of 

 energy linkage in the process, as discussed this morning, but the rea- 

 son why the salt molecules all move in one direction— toward the in- 

 terior of the cell— eludes us. As far as I am concerned, the central 

 problem of evolution, which is the progression toward more and more 

 complex forms, is another expression of polarity. Polarity is the basis 

 for the separation of head and tail. It causes differentiation and is very 



