The leaves are scattered, stipulate, or have at least a well developed
sheath, which is generally prolonged on each side into a free
portion (“adnate stipules”). The flowers are regular, _perigynous_
or _epigynous_. Calyx and corolla 5 (-4)-_merous_ with the usual
position. The corolla is always polypetalous. The stamens are present
in very varying numbers (5–∞) and position, but _always_ placed in
5-_or_ 10-_merous whorls_; they _are frequently_ 20 in 3 whorls (10
+ 5 + 5; see Figs. 494, 502, 505); the nearer they are placed to the
circumference, the longer they are; they are generally _incurved in the
bud, or even rolled up_. The number of the carpels is from 1–∞; in most
cases all are _individually free_ (syncarp), and when they are united
it is in every case with the ovaries only, whilst the _styles_ remain
more or less _free_ (_Pomaceæ_, species of _Spiræa_). The _seeds_ have
a straight embryo, and usually no endosperm.
The perianth and stamens are most frequently _perigynous_ on
the edge of the widened receptacle; its form varies between a
flat cupule and a long tube or a cup (Figs. 495, 496, 498, 499,
500); the carpels are situated on its base or inner surface, in
some instances on a central conical elongation of the floral
axis (Fig. 496). The carpels in _Pomaceæ_ also unite more or
less with the hollow receptacle, or this grows in and fills up
the space between the carpels, so that a more or less epigynous
flower is formed (Fig. 504).--The following numbers of _stamens_
occur: 5, 10 (in 1 whorl), 15 (10 + 5), 20 (10 + 5 + 5), 25 (10
+ 10 + 5), 30-50 (in 10-merous whorls)--compare the diagrams.
The theoretical explanation of this relation of the 10-merous
whorls and their alternation with the 5-merous whorls is not
definitely determined; a splitting of the members of the
5-merous whorls may be supposed, but the development shows no
indication of this, and it is not supported in any other way.
Several genera have “_gynobasic_” styles, that is, the style
springs from the base of the ovary (Fig. 497 _A_, _B_).
The Rosifloræ are on one side closely related to the
Saxifragaceæ (especially through _Spiræa_) from which it is
difficult to separate them, and to the Myrtifloræ; on the other
side they are allied, through the Mimosaceæ with the large
number of stamens, and through the Amygdalaceæ with its single
carpel, to the Leguminosæ. The family begins with forms which
have many-seeded follicles, and passes on the one side to forms
with nuts and drupes in perigynous flowers, and on the other
side to the Pomaceæ.
Order 1. =Rosaceæ.= Herbs or shrubs, generally with compound leaves and
persistent (adnate) stipules, flower _perigynous_, _gynœceum formed of
many free_ (therefore oblique) _carpels, syncarps_ with fruitlets of
various kinds. The exceptions are noted under the genera.
[Illustration: FIG. 494.--Diagram of _Comarum palustre_.]
[Illustration: FIG. 495.--Flower of _Spiræa lanceolata_.]
=1.= SPIRÆEÆ (Fig. 495) has 2–many ovules in each ovary, while in the
other groups there is generally only 1, and never more than 2 ovules in
each loculus. There are generally 5 _cyclic_ carpels and the fruit is
5 _follicles_, which are not enclosed by the receptacle. The majority
are shrubs. Stipules are often wanting.--_Spiræa_ (Meadow-Sweet).
The flowers are generally borne in richly flowered inflorescences
of various forms. The carpels, in some species, unite together
and form a _simple_ gynœceum with free styles (an approach to the
_Pomaceæ_).--~Closely allied to _Spiræa_ are the East Asiatic shrubs:
_Kerria japonica_, which has solitary flowers, in this country nearly
always double (the fruit a nut), and _Rhodotypos kerrioides_ which
has opposite leaves, a remarkable feature among the Rosifloræ; it has
a 4-merous flower, a well developed disc inside the andrœcium, and a
drupe. Closely allied also is _Gillenia_ (N. Am.) differing chiefly
in the ascending ovules, _Spiræa_ having pendulous ovules, and a more
tubular receptacle.~
The groups _Quillajeæ_ and _Neuradeæ_ form a transition from
_Spiræa_ to _Pomaceæ_. In the first group, which contains only
trees or shrubs with generally simple leaves, the carpels are
either free or united (into a capsule); in the second the
receptacle unites with the carpels, which are themselves often
united together; in this case, too, the fruit is a capsule.
_Quillaja_ (S. Am.); _Exochorda_ (China).
=2.= POTENTILLEÆ (Figs. 494, 496, 497). The flower has an “_epicalyx_”
(Fig. 494 _C_) alternating with the sepals and formed by their
stipules which are united in pairs, and hence its leaves are often
more or less deeply bifid. The receptacle is cupular and often quite
insignificant. The sepals are valvate in the bud. The large number of
fruitlets are _achenes_, borne on a well-developed convex portion of
the receptacle (~the Ranunculeæ resemble the Potentilleæ, but have
no epicalyx, no enlarged receptacle, and spirally-placed stamens~).
Most of the species are herbs with dichasial inflorescences, often
arranged in racemes.--_Potentilla_ (Cinquefoil). The achenes are
borne on a _dry_, hairy receptacle; the style is situated towards
the apex of the ovary, and is not prolonged after flowering. Herbs
with digitate, in some, however, pinnate leaves, and generally yellow
flowers.--_Comarum_ (Fig. 494) (Marsh Cinquefoil) forms, by its
fleshy-spongy receptacle, a transition to the next genus.--_Fragaria_
(Strawberry) (Fig. 496). The receptacle becomes finally fleshy,
coloured, and falls off (biologically it is a berry); the numerous
fruitlets (drupes with thin pericarp) have basal styles (Fig. 497);
leaves trifoliate; long, creeping runners.--_Geum_ (Avens) has a
terminal style which after flowering elongates into a long beak, with
the apex (after the uppermost part has been thrown off) bent back into
a hook, thus furnishing a means of distribution for the fruits. Leaves
pinnate.--~_Dryas_ comprises 3 Arctic or Alpine species with simple
leaves and solitary flowers, the calyx and corolla 8–9-merous, the
fruit resembles that of _Geum_, but the styles become still longer and
feather-like (a flying apparatus).~
[Illustration: FIGS. 496, 497.--_Fragaria vesca._
FIG. 496.--Longitudinal section of flower.