704 PATTERNS AND PROBLEMS OF DEVELOPMENT 



of machines with specific locahzed parts. There are quantitative "ma- 

 chines" which can be divided into parts indefinitely, and each part pos- 

 sesses the characteristics of the whole, only on a smaller scale. A flowing 

 stream, an electric current in a conductor, and, to a considerable extent, 

 a flame are such machines. If axiate organismic pattern is primarily a 

 quantitative gradient pattern, the organism in its simplest terms is a 

 quantitative machine in a specific protoplasm. Parts capable of becoming 

 wholes when isolated differ from the wholes only quantitatively, as far 

 as the factors essential to reconstitution are concerned; if qualitative re- 

 gional differences are present, they are not essential. As a matter of fact, 

 we know that they are often obliterated. The pattern in an isolated part 

 may differ in scale from that of the whole, according to physiological and 

 external conditions; scale of organization may be larger than the piece, so 

 that a partial axiate pattern results, or smaller than the piece, so that a 

 single axiate pattern does not involve the whole piece. These and many 

 other experimental data are diflicult to interpret on any other basis than 

 a primarily quantitative gradient pattern. 



Objection to a theory of origin of organismic pattern in relation or reac- 

 tion to conditions external to the protoplasm concerned has been made on 

 the ground that features of pattern so constant and fundamental as polar- 

 ity and symmetry cannot be determined by external factors, though they 

 may be modified by such factors. To the theory that metabolism is the 

 essential factor in the establishment of pattern the objection has also 

 been raised that a fixed persistent pattern becoming the basis of morpho- 

 logical development cannot originate in activity, in metabolism, alone. 

 These objections ignore certain important points. First, external factors 

 in their action on living protoplasms only initiate changes; the results 

 depend on the specific constitution and physiological condition of the 

 protoplasm concerned. The physiological condition of the protoplasm is 

 not independent of environment, but within the "normal" range an ap- 

 proach to a steady state is possible. If local action of an external factor 

 determines a local activation and a gradient results, or if an external dif- 

 ferential determines a gradient directly, the characteristics of the gra- 

 dient, its length, its steepness, the reactions occurring in it, and the spe- 

 cific or qualitative differences which develop at its different levels will all 

 depend primarily on the constitution of the protoplasm acted upon, rather 

 than on, the acting agent. The egg of Fucus is an excellent illustration. 

 Polarity may be determined in it by differential illumination, by electric 

 current, by a differential in hydrogen-ion concentration, by a stratification 



