Protection mechanisms are also important, as birds are
large and potentially destructive pollinators. A common
form of protection is provided by mechanical strengthening
of the flower by the formation of sclerenchyma or
collenchyma tissue in various floral parts. The ovary and
ovules, often situated near to the nectaries, are particularly
vulnerable to the probing of bird’s beaks. Protection of
ovules takes many forms. There may be separation of
ovary and nectary, either by the sheathing of the ovary by
a staminal tube, or by a stalked or inferior ovary.
Alternatively, there may be a groove formed by the
corolla to guide birds’ beaks to the nectary without
causing damage, or ridges of the corolla to provide direct
protection to the ovary. In addition, the style may be
protected in a groove formed from ridges of the upper
petals, as in Justicia californica (Benth.) D. Gibson. In
Penstemon it is the nectaries rather than the ovary that
shift. In bird-pollinated species, the nectaries are displaced
upwards from the base of the ovary to the outer bases of
the upper pair of stamens.