ECCENTRIC GROWTH. 271 



is probably to be regarded as a special case of construction evolved 

 by secondary specialisation for a special set purpose, — the exist- 

 ence of a capacity for becoming symmetrical being the essential 

 character which may be increased by natural selection, — so again, 

 in the case of centric and eccentric construction, a tendency 

 toward eccentricity would be expected, in that it presents the most 

 general mathematical construction ; while the chances that nutri- 

 tion or circumstances of environment would not be absolutely 

 constant on all sides of the organism are enormously greater than 

 those of uniformity. 



The essential question is rather, Is there such a thing as 

 absolutely centric growth at all in nature ? Hypotheses of 

 centric growth have been read into the plant as presenting simple 

 mathematical cases ; but should not the eccentric be rather taken 

 as the starting-point, since, by assuming a simple case which is 

 not the primitive one, the subject may be approached from a 

 misleading point of view ? The marvel is, in fact, not that some 

 shoot systems should show marked eccentricity of growth, but 

 that any should ever approximate the centric, unless the inherent 

 growth faculty of the organism in working out its specific form 

 according to simple laws of growth is, as a rule, far stronger than its 

 tendency to respond to external stimuli. However, the fact remains 

 that the difference between centric and eccentric growth pheno- 

 mena is only loosely judged by the eye, which is not a mathe- 

 matical guide, and for practical purposes growth is often so 

 approximately centric that there is no harm in calling it so, so 

 long as it is remembered that it is not possible to draw a sharp 

 distinction between the two cases by actual observation. 



So far as eccentricity of growth may be induced by inequality 

 in the action of external stimuli, such as light and gravity, quite 

 apart from the equally possible conception of inherent irregularity 

 of construction, it becomes clear that every lateral flower shoot, 

 borne on an erect axis, would have a natural tendency to become 

 eccentric, just as every lax shoot which is not strong enough to 

 support its own weight. A tendency to more or less obvious 

 zygomorphy should, for example, be the rule in any short lateral 

 floral axis, and not the exception ; and here again with no reference 



