STRUCTURES RESEMBLING ORGANIC GROWTHS. l6l 



physiological constitution of the system, which would be regained 

 after disturbance. I introduce this abstract conception of the 

 organic equilibrium in order to suggest a general point of view 

 from which the actual phenomena of form-regulation may per- 

 haps be considered to advantage. There is much evidence 

 indicating that many structural correlations are controlled by 

 electrolytic processes of the above kind. 



Morphallaxis is essentially a phenomenon of form-correlation, 

 which is exemplified by the third type of process mentioned 

 above, in which the growth of one part may be promoted or 

 inhibited by growth in another part more or less distant from the 

 first. For example, in plants the development of new buds or 

 roots is prevented so long as the main growing tip or root-system 

 is intact; formative inhibitions of this type are extremely fre- 

 quent ; hence the isolation of an organ, by removing the inhibiting 

 influence of other parts, may cause the development of roots, 

 shoots, or other organs of a kind entirely different from itself, 

 The whole organism may thus be reproduced in certain cases; 

 the leaves of Begonia and Bryophyllum furnish the most striking 

 instances of this phenomenon. In plants the normal correlation 

 between the growth of different organs appears to depend 

 largely on this influence. In the lower animals various regions 

 or parts of the organism are also capable of reconstituting the 

 whole when removed from the influence of other regions. In 

 many axiate animals the more anterior regions thus "dominate" 

 the more posterior regions, and a gradient of influence exists, 

 as shown in detail by Child in his recent remarkable book. 1 

 The controlling influence is greatest near the dominant region 

 and decreases with increasing distance, so that a sufficient degree 

 of isolation for independent development may often result from 

 simple increase in length; e. g., in a planarian or a hydroid stem 

 the portion of the animal most distant from the head end or the 

 hydranth may form a new individual while still connected with 

 the parent. According to Child, individuation in either asexual 

 or sexual reproduction consists essentially in the removal of one 

 region of the organism from the growth-inhibiting influence of 

 other regions; the region thus physiologically isolated then 



^'Senescence and Rejuvenescence," especially Chapter 9. See also the same 

 author's "Individuality in Organisms." 



