The changes are, _of course_, brought about by a "nutritional" process, and the symmetry is undoubtedly the result of a "balance of forces," but to say so is a truism.

The question is, what is the cause of this "nutritional balancing"?
It is here contended that it must be due to an internal cause which at present science is utterly incompetent to explain.

It is an internal property possessed by each living organic whole as well as by each non-living crystalline mass, and that there is such internal power or tendency, which may be spoken of as a "polarity," seems to be demonstrated by the instances above given, which can easily be multiplied indefinitely.
Mr.Herbert Spencer[195] (speaking of the reproduction, by budding, of a Begonia-leaf) recognizes a power of the kind.

He says, "We have, therefore, no alternative but to say that the living particles composing one of these fragments have an innate tendency to arrange themselves into the shape of the organism to which they belong.

We must infer that a plant or animal of any species is made up of special units, in all of which there dwells the intrinsic aptitude to aggregate into the form of that species; just as{185} in the atoms of a salt, there dwells the intrinsic aptitude to crystallize in a particular way.