THE USES AND ORIGIN OF THE ARRANGEMENTS OF LEAVES IN PLANTS. • 411 



be distinct, as we have found that it otight to be, from the origin of the 

 relations in the parts of whorls to one another, and to those of adjacent 

 whorls. These would be results of a subsequent segmentation, and would be 

 determined by the utilities which we have considered in this and in the spiral 

 arrangements. And so both this and the spiral arrangements as general types 

 of structure, though originating, as P have supposed, in useful relations to for- 

 mer conditions of existence, may be regarded in relation to later developments 

 as useless, and merely inherited or genetic types; the bases on which subse- 

 quent utilities had to erect existing adaptations of structure. The segmentation 

 of the single spiral frond would at first have little or no relation to these 

 more refined utilities of arrangement, but out of all the variable and possible 

 arrangements so produced there would be a gradual selection, and a tendency 

 toward the prevalence of those special forms, which are at present the most 

 common ones. The typical or unique angle of the theory of Phyllotaxy would 

 thus appear to be the goal toward which they tend, rather than the origin 



* 



of the spiral arrangements. But since a simple cyclic arrangement appears to 

 have also an important value, we cannot concede to the typical angle the 



exclusive dignity of even this position. 



The segmentation I have supposed in this process should not be regarded 

 as an hypothetical element in it; since it is a well-established law of develop- 

 ment. Distinct organs are not separately produced from the beginnings of their 

 growth, but make part of their progress in conjunction, or while incorporated 

 in forms, from which they become afterwards separated; and become then more 

 and more special in their characters, or different from other parts. It is this 

 differentiation and separation of parts out of already grown wholes which dis- 

 tinguishes development from mere growth. The analogy of the phases of 

 development in embryonic or germinal life to development in general is liable, 

 however, to be carried too far; and the fact is liable to be overlooked, that 

 these phases of growth are special acquisitions of the higher forms of life, 

 which have features of adaptation peculiar to them. But the more general 

 features of them, and the useless, or merely genetic phases, may safely be 

 regarded as traces of past characters of adaptation, which a change in the 

 mode and order of individual development has not obliterated; while new 

 adaptations have been added, that have no relation to any past or simpler 

 forms of life, but only to the advantages which embryonic or germinal modes 

 of reproduction have secured. If we should follow out the phases of general 



