In such cases they
are searched for with perseverance, and the fact of their rarity
impresses itself strongly on our mind.
Twisted stems are selected as a first example. This monstrosity, called
_biastrepsis_, consists of strongly marked torsions as are seen in many
species with decussate leaves, though as a rule it is very rare. Two
instances are the most generally known, those of the wild valerian
(_Valeriana officinalis_) and those of cultivated and wild sorts of
teasels (_Dipsacus fullonum_, _D. sylvestris_, and others). Both of
these I have cultivated during upwards of fifteen years, but with
contradictory results. The valerian is a perennial herb, multiplying
itself yearly by [403] slender rootstocks or runners producing at their
tips new rosettes of leaves and in the center of these the flowering
stem. My original plant has since been propagated in this manner, and
during several years I preserved large beds with hundreds of stems, in
others I was compelled to keep my culture within more restricted limits.
This plant has produced twisted stems of the curious shape, with a
nearly straight flag of leaves on one side, described by De Candolle and
other observers, nearly every year. But only one or two instances of
abnormal stems occurred in each year, and no treatment has been found
that proved adequate to increase this number in any appreciable manner.
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