The ablest systematists prefer to
consider the ordinary species as collective groups, calling their
constituents "The elements of the species," as was done by A.P. De
Candolle, Alph. De Candolle and Lindley.
By this method they clearly point out the difference between the
subdivisions of wild species as they ordinarily occur, and the varieties
in our gardens, which would be very rare, were they not singled out and
preserved.
Our familiarity with a character and our grounds for calling it an old
acquaintance may result from two causes, which in judging a new [130]
variety are essentially different. The character in question may be
present in the given species or it may be lacking, but present in the
other group. In the first case a variety can only be formed by the loss
of the character, in the second case it arises by the addition of a new
one.
The first mode may be called a negative process, while the second is
then to be designated as positive. And as it is more easy to lose what
one has than to obtain something new, negative varieties are much more
common than are positive ones.
Let us now take an instance of a character that is apt to vary in both
ways, for this is obviously the best way of making clear what is meant
by a negative and a positive change.
In the family of the composites we find a group of genera with two forms
of florets on each flower-head.
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