ute of petals, or nearly so,
with a single, generally imperfect anther; the carpels also are more or
less imperfect, but not sufficiently so to prevent some seeds from being
formed. A similar production of imperfect flowers has been noticed in
many other orders, _e.g._ _Violaceae_, _Campanulaceae_, &c. In some cases
these supplementary blossoms are more fertile and prolific in good seeds
than are the normally constructed flowers. M. Durieu de Maisonneuve
alludes to a case where flowers of this description are produced below
the surface of the ground. The plant in question is _Scrophularia
arguta_, and it appears that towards the end of the summer the lowest
branches springing from the stem bend downwards, and penetrate the soil;
the branches immediately above the lowest ones also bend downwards, but
do not always enter the earth. These branches bear fertile flowers:
those which are completely below the soil are completely destitute of
petals; those which are on the surface have a four-lobed corolla whose
divisions are nearly equal, like those of _Veronica_.[369]

To Sprengel, and specially to Darwin, physiologists are indebted for the
demonstration of the relation of di- and trimorphic flowers to
fertilisation. In certain genera of orchids, such as _Catasetum_, &c.,
flowers of such different form are produced that botanists, without
hesitation, considered them as belonging to different genera, until the
fact of their occasional production on the same plant showed that they
were not of even specific importance. It was reserved for Mr. Darwin to
show experimentally that these very different flowers are really sexual
forms of one and the same species, ordinarily occurring on different
plants, i.e. dioecious, but occasionally formed on the same spike. The
same excellent observer has demonstrated that the di- and trimorphic
forms of _Primula_, of _Linum_, _Lythrum_, and other plants--forms
differing mainly in the relative length of the stamens and styles, are
also connected with striking differences in the number of perfect seeds
produced. The most perfect degree of fertility is obtained when the
stigma of one form is fertilised by the pollen taken from stamens of a
corresponding height. On the other hand, when the union is, as Mr.
Darwin states, illegitimate, that is, when the pollen is taken from
stamens not corresponding in length to the style, more or less complete
sterility ensues in the progeny, sometimes even utter inf