lar form may rather be due to dilatation
than to cohesion. M. Kickx[16] mentions an instance of the kind in the
leaves of a species of _Nicotiana_, and also figures the leaf of a rose
in which two opposite leaflets presented themselves in the form of
stalked cups. Schlechtendal[17] notices something of the same kind in
the leaf of _Amorpha fruticosa_; Treviranus[18] in that of _Aristolochia
Sipho_.

M. Puel[19] describes a leaf of _Polygonatum multiflorum_, the margins
of which were so completely united together, as only to leave a circular
aperture at the top, through which passed the ends of the leaves. The
Rev. Mr. Hincks, at the meeting of the British Association at Newcastle
(1838), showed a leaf of a Tulip, whose margins were so united that the
whole leaf served as a hood, and was carried upwards by the growing
flower like the calyptra of a Moss.

The margins of the stipules are also occasionally united, so as to form
a little horn-shaped tube. I have met with instances of this kind in the
common white clover, _Trifolium repens_, where on each side of the base
of the petiole the stipules had the form just indicated. That the bracts
also may assume this condition, may be inferred from the peculiar
horn-like structures of _Marcgraavia_, which appear to originate from the
union of the margins of the reflected leaf.

=Tubular petals= occur normally in some flowers, as _Helleborus_,
_Epimedium_, _Viola_, &c., and as an exceptional occurrence I have seen
them in _Ranunculus repens_, while in _Eranthis hyemalis_ transitions
may frequently be seen between the flat outer segments of the perianth
and the tubular petals. To Dr. Sankey, of Sandywell Park, I am indebted
for the flower of a Pelargonium, in which one of the petals had the
form of a cup supported on a long stalk. This cup-shaped organ was
placed at the back of the flower, and had the dark colour proper to the
petals in that situation. I have seen a petal of Clarkia similarly
tubular, while some of the cultivated varieties of _Primula sinensis_
exhibit tubular petals so perfect in shape as closely to resemble
perfect corollas.

[Illustration: FIG. 9.--_Eranthis hyemalis_. Transition from flat sepal
to tubular petal.]

Like the petals, the stamens, and even the styles, assume a hollow
tubular form. This change of form in the case of the stamens is, of
course, usually attended by the petaloid expansion of the filament, or
anther, and the more or less complete