456 Morpho genetic Factors 



where such a pattern is passed from one generation to the next in the 

 ectoplasmic striping, which is divided between the daughter cells. Tartar 

 concludes that "it is possible that the complex activities of the cyto- 

 architecture of stentor may forecast an appreciation that some homologous 

 cytoplasmic pattern is common to all cells and is as important in its way 

 as the chromosomal nucleus which also has its orderly arrangements." 



How such configurations originate is not clear, but some biologists, 

 among them Needham (1936), look for suggestions to the paracrystalline 

 state of matter ( "liquid crystals" ) . The molecular solutes in most solutions 

 are distributed at random but in some it can be shown that these dis- 

 solved particles are arranged in a very regular fashion. This may de- 

 termine such cellular events as differential growth and plane of division 

 and thus provide a basis for organic orderliness. 



A number of workers, among them Baitsell (1940), have gone still 

 further and endeavor to translate molecular pattern into cellular pattern. 

 The molecule is a specific and organized structure. Perhaps, so goes the 

 argument, the forces that pull the atoms together into the orderly con- 

 figuration shown by a large and complex protein molecule, for example, 

 are of the same nature as those that bind together a vast number of such 

 molecules into the system which is a living cell, the unitary structure of 

 all organisms. On such a hypothesis the cell is to be looked upon as an 

 enormous molecule. If this concept is carried one step further, the whole 

 organism might be regarded as a single molecule and integrated by the 

 same forces that organize simpler ones. 



A promising hypothesis has come from Turing (1952), who suggests 

 that a homogeneous system of substances which react on each other and 

 are diffusing through a tissue may become unstable because of random 

 disturbances in it and may thus produce a pattern. Turing analyzes a 

 hypothetical example mathematically and shows that six different forms 

 may result from a simple "diffusion-reaction" system of this sort. He seeks 

 a mechanism by which genes determine structure and suggests that well- 

 known physical laws, with their mathematical implications for develop- 

 ment, are enough to account for many of the phenomena of organic 

 form. Wardlaw (1953a, 1955c) has written a constructive discussion of 

 Turing's rather involved theory and its applications to morphogenetic 

 problems in plants. 



Rashevsky in a series of papers (1944, 1955, 1958, and others) has 

 approached the problems of biology from a physical and especially a 

 mathematical point of view and in particular has endeavored to interpret 

 biological processes in terms of position and relation. 



The problems of growth and form have been discussed by Sir D'Arcy 

 Thompson in his classic volume by that name (1942) already mentioned 

 frequently in this book. He marshals evidence from physics, chemistry, 



