In all of these directions we see that the differentiating marks show
more or less clearly that they are built up of units. Allied forms are
separated from each other without intermediates. Transitions are wholly
wanting, although fallaciously apparent in some instances owing to the
wide range of fluctuating variability of the forms concerned, or to the
occurrence of hybrids and subvarieties.
These physiologic units, which in the end must be the basis for the
distinction of the systematic units, may best be designated by the term
of "unit-characters." Their internal nature is as yet unknown to us, and
we will not now look into the theories, which have been propounded as to
the probable material basis underlying them. For our present purpose the
empirical evidence of the general occurrence of [250] sharp limits
between nearly related characters must suffice. As Bateson has put it,
species are discontinuous, and we must assume that their characters are
discontinuous also.
Moreover there is as yet no reason for trying to make a complete
analysis of all the characters of a plant. No doubt, if attained, such
an analysis would give us a deep insight into the real internal
construction of the intricate properties of organisms in general. But
taxonomic studies in this direction are only in their infancy and do not
give us the material required for such an analysis.
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