onfiguration,
subject only to slight variations, dependent upon age, conditions of
growth, &c. The cotyledons are very uniform in shape in each plant, and
are scarcely ever subject to variation. The leaves near the base of the
stem, the root-leaves as they are not unfrequently called, sometimes
differ in form from the stem-leaves; these again differ from the bracts
or leaves in proximity to the flower. The floral envelopes themselves,
as well as the bud-scales, all have their own allotted form in
particular plants, a form by which they may, in most cases, be readily
recognised. Hence, then, in the majority of plants there is naturally
very considerable difference in the form of the leaf-organs, according
to the place they occupy and the functions they have to fulfil; but, in
addition to this, it not unfrequently happens that the leaf-organs in
the same portion of the stem are subject to great variation in form.
This is the condition to which the term heterophylly properly applies.
The variation in form is usually dependent on a greater or less degree
of lobing of the margin of the leaf; thus, in the yellow jasmine, almost
every intermediate stage may be traced from an ovate entire leaf to one
very deeply and irregularly stalked. _Broussonettia papyrifera_, and
_Laurus Sassafras_, and the species of _Panax_, may be mentioned as
presenting this condition. Sometimes in the last-named genus, as also in
_Pteridophyllum_, every gradation between simple and compound leaves may
be traced. The horse-radish (_Cochlearia Armoracia_) may also be
instanced as a common illustration of polymorphism in the leaves. In
ferns it is likewise of frequent occurrence, markedly so in
_Scolopendrium D'Urvillei_, in which plant every gradation from a simple
oblong frond to an exceedingly divided one may be found springing from
the same rhizome at the same time.

[Illustration: FIG. 177.--_Syringa persica laciniata_, showing
polymorphous leaves.]

A similar protean state, but little less remarkable, occurs in many of
our British ferns, notably in _Scolopendrium vulgare_, of which Mr.
Moore enumerates no fewer than 155 varieties,[366] many of the forms
occurring on the same plant at the same time. Cultivators have availed
themselves of this tendency to produce multiform foliage, not only for
the purposes of decoration or curiosity, as in the many cut-leaved or
crisped-leaved varieties, but also for more material uses, as, for
instance, the many