320 EMBRYOGENESIS IN PLANTS 



definite micro-structure of some kind, in which complex reactions not 

 only take place, but take place in an orderly manner. At some future 

 time it may be that this specific protoplasmic organisation will be 

 partially defined in terms of physical chemistry; meanwhile, as 

 Needham (1942) and Woodger (1945) have emphasised, there is need 

 for a theory of zygote structure, in addition to the theory of the gene, 

 to explain embryological data. In the view of Needham and others, 

 the way in which a young embryo develops is determined by the proto- 

 plasmic organisation of the fertilised ovum. That such organisation 

 exists is indicated by experimental and other evidence, but its nature 

 cannot yet be defined. Studies of centrifuged eggs have suggested that 

 the ovum contains a framework of a viscid protoplasmic substance 

 which can recover its normal form after distortion; and it is known 

 that the eggs of some species may develop normally after their movable 

 ingredients have been stratified. In some eggs, however, the cytoplasm 

 may apparently flow like a liquid. Needham envisages the protein 

 chains of the protoplasmic lattice as being 'connected at many points 

 by residual valencies and relatively loose attachments' and as being 

 capable of springing back into position after disarrangement. This he 

 refers to as dynamic structure in protoplasm. Schleip (1929) has 

 pointed out that in every attempt to explain the polarity and symmetry 

 of eggs 'some as yet unknown property of the protoplasm has to be 

 introduced.' He refers to this property as the intimate structure of the 

 protoplasm. Needham has indicated the kinds of theories and facts 

 that may contribute towards an understanding of the intimate structure. 

 Liquid crystals, i.e. substances in the paracrystalline state, may be 

 important, because (he says) 'hving systems actually are liquid crystals, 

 or, it would be more correct to say, the paracrystalline state undoubtedly 

 exists in living cells' (1942, p. 661). Paracrystalline substances have 

 elongated molecules which can be distributed or arranged in different 

 ways, regular and irregular, according to the conditions in which they 

 exist: the molecules may be completely at random, as in the true 

 isotropic liquid state, or they may be disposed in different patterns 

 with a high degree of regularity in the crystalline solid state. The 

 protoplasmic organisation at any particular time is also of the greatest 

 importance in determining the competence of cells to react to morpho- 

 genetic and other stimuli. 



Child (1941, p. 694) agrees that living protoplasts and the skeletal 

 materials (cell walls) do yield remarkable evidence of a definite mole- 

 cular or micellar structure and orientation {see also Frey Wyssling, 

 1948). Change of pattern of proteins in relation to tension can also be 

 demonstrated and there is evidence of molecular orientation to surfaces 

 and interfaces. But, in Child's view: 'Protoplasms in general have not 



