316 RELATION OP PHYLLOTAXIS TO MECHANICAL LAWS. 



VI. Varying Growth in Lateral Members. 



So far, it may be noted, all secondary changes, whether those 

 included under the previous headings of secondary pressure 

 effects or phenomena of bilaterality, have for their result the 

 obliteration of the theoretical log. spiral construction figure, and 

 tend to obscure the primary system. To such an extent, and 

 so rapidly, does this deformation usually take place, that the 

 primary theoretical construction for the distribution of growth 

 becomes increasingly difficult of accurate observation; and it is 

 clear that the special case of bilaterality is but one of a large series 

 of phenomena in which varying rates of growth produce secondary 

 displacement effects. While, in fact, these special cases of 

 " dorsiventrality '' and "phyllody" include the disturbances set 

 up in the system consequent on varying rates of growth in 

 different planes in the primordia themselves, other variations 

 are also possible, and may be comprised more especially under 

 two main sections : — 



(1) Varying rates of growth between the axis and the primordia. 



(2) Varying rates of growth in the primordia at different 



portions of their length. 

 That is to say, although the log. spiral construction was founded 

 on a physical and mathematical conception — the assumption of 

 a uniform growth-expansion in the protoplasm of the shoot-apex — 

 it does not necessarily follow that such a uniform rate of growth 

 is actually present to any great extent in the growing-point of 

 any given plant, any more than that all radially constructed stems 

 should prove to be mathematically circular in section. The case 

 of uniform growth, however, requires to be considered first, just 



