ORIGINS OF EMBRYONIC PATTERNS 699 



To the extent that chemical reaction takes place, the crystal pattern dis- 

 appears; chemical reaction is an essential feature of pattern in organisms. 

 That organismic pattern originates in a crystalline space lattice appears 

 on the basis of the evidence extremely improbable, but that crystalline 

 structures and molecular orientations appear in organisms is evident, and 

 the evidence indicates that they are secondary effects of the pattern. 

 Some of them are evidently determined by purely local conditions and 

 are only remotely related to the general pattern; others are more directly 

 related to that pattern. Probably molecular or micellar orientation is 

 very generally characteristic of fibrillar structures and of various particles, 

 inclusions, and metabolic products. Mechanical tension and pressure may 

 bring about orientation of molecules or particles, orientation may occur 

 in relation to interfaces and to flow, and some protoplasms may become 

 crystalline; but there is, at present, no evidence for, and much against, 

 the concept of organismic pattern as primarily a pattern of molecular 

 structure and orientation. Such concepts seem to put the cart before the 

 horse. 



Some or all of the specific asymmetries of unicellular forms, spermato- 

 zoa, etc., discussed in the preceding chapter, and perhaps many of the 

 more minute structural features in multicellular forms, may be expressions 

 of a molecular or crystalline structure; but it may again be emphasized 

 that, in general, they appear to represent more nearly ends than begin- 

 nings of development and that they develop in definite relations to more 

 general patterns of earlier stages. If a structural factor of this sort is in- 

 volved in lateral asymmetries of multicellular forms, it also is apparently 

 a derivative of developmental pattern; but the evidence available sug- 

 gests that lateral asymmetry is a physiological gradient pattern. 



More or less definite patterns on a molar scale appear in many inorganic 

 systems quite independently of any molecular pattern of the whole. For 

 example, any particular region of a flowing stream shows a definite pat- 

 tern of flow of water, erosion or deposition, and morphology of banks and 

 bed. This pattern develops from the activity of the water in relation to 

 gravity, an environmental factor, and to the banks and bed. The mo- 

 lecular pattern of the water undergoes continuous change; the banks and 

 bed may consist of various substances — sand, clay, and rock of different 

 kinds — with many different molecular patterns, but the general morphol- 

 ogy of the stream depends on the conliguration of banks and bed and 

 energy of flow rather than on molecular pattern of any of the stream 

 components. In "normal" environment, that is, within certain limits of 



