The flowers are _regular_, ☿, _hypogynous_, and gamopetalous. The
_stamens_ are _equal in number_ to the petals (Fig. 547) and _are
placed opposite to them_. The ovary is _unilocular_, with _a free,
central_ placenta with 1–many ovules.--The flower is a further
development of the Diospyrinæ; the suppression of the calyx-stamens,
which commenced in this family, is carried further in the Primulinæ,
so that in the majority of cases no trace of them is present, but
in certain species and genera (_Samolus_, _Lysimachia thyrsiflora_,
_Soldanella_, certain Myrsineæ) some small bodies (scales, teeth,
etc.) are found in the position of the suppressed stamens. Again, the
lateral portions of the carpels are suppressed, so that the _ventral
placentæ_ with the ovules are separated from the dorsal portions, and
_are united into a free central placenta_; this theory is supported by
the branching of the vascular bundles, the development, and various
comparative considerations.--Sn, Pn, A0 + n, Gn; where n = 4–8,
generally 5. The carpels are placed opposite the sepals (Fig. 547).
Order 1. =Primulaceæ= (=Primroses=). This order has _many ovules_
attached to a _thick, free, central placenta_ (Fig. 547); _style
undivided_ with a _capitate_ stigma; ovules semi-anatropous; fruit a
_capsule_ with many seeds.
All the plants belonging to this order are _herbs_; stipules wanting;
the flower is most frequently 5-merous (S5, P5, A0 + 5, G5; except
_Centunculus_ and _Trientalis_). The corolla and capsule have various
forms, but the capsule generally opens by teeth at the apex. The ovules
are semi-anatropous (in _Hottonia_ they are anatropous), and the seeds
are therefore _peltate_, with the hilum situated in the centre of one
side. The endosperm is fleshy or horny. The flowers are borne either in
racemes or in umbels; as _bracteoles are typically_ absent (Fig. 547),
cymose branching does not occur.
[Illustration: FIG. 548.--_Primula_: dimorphic flowers. _A_
short-styled; _B_ long-styled.]
[Illustration: FIG. 549.--_Cyclamen persicum._]
_Primula_ (Primrose) has most frequently a vertical rhizome, bearing
a rosette of leaves at its summit, and long-stalked umbels; corolla
_rotate_ or slightly funnel-shaped; the capsule opens at the apex by 5
_teeth_. The flowers in some species are heterostyled (long-styled or
short-styled; Fig. 548). Closely allied are _Androsace_ (with ovate,
cup-shaped corolla-tube and ligular scales, alternating with the
corolla-lobes) and _Soldanella_ (funnel-shaped corolla with laciniate
lobes and most frequently ligular scales).--_Hottonia_ (Water-Violet)
is an aquatic plant with pectinate leaves and heterostyled
flowers.--_Cortusa._ _Dodecatheon._ _Cyclamen_ (Fig. 549) has solitary,
long-stalked flowers, and a rotate corolla with the lobes reflexed; the
stalk of the capsule rolls up spirally; the tuberous rhizome is formed
by the hypocotyledonary internode. Only 1 cotyledon.--_Lysimachia_
(Money-wort); stem-internodes well developed, leaves opposite or
verticillate, calyx almost polysepalous, corolla deeply 5-partite (Fig.
550). The flowers are solitary or in racemes.--_Anagallis_ (Pimpernel),
leaves opposite, flowers solitary; the fruit a pyxidium (Fig. 551);
similarly in _Centunculus_, which is 4-merous.--_Trientalis_, the
flowers are most frequently 7-merous.--_Glaux_ (Sea Milk-wort) is a
creeping maritime plant with opposite leaves; flowers solitary in the
leaf-axils, _corolla absent_, but with coloured calyx. ~The petals are
usually developed later than the stamens in the Primulaceæ; but in
this instance they are entirely suppressed.~--_Samolus_ (Brookweed)
differs from all the others in having an _epigynous_ flower;
barren sepal-stamens are also present. The bracts in the racemose
inflorescences are displaced along the flower-stalks.
[Illustration: FIG. 550.--_Lysimachia thyrsiflora._]
[Illustration: FIG. 551.--_Anagallis arvensis._ Fruit dehiscing.]
POLLINATION. Insect-pollination in the majority;
cross-pollination is promoted in some by heterostyly (Fig.
548).--300 species; especially in northern temperate zones;
the majority on mountains (_Soldanella_, _Androsace_, etc.);
almost absent in the Tropics. A large number are ORNAMENTAL
PLANTS, _e.g._ _Primula auricula_ (from the Alps), _P. sinensis_
(China), _P. elatior_ (Oxslip, a native) and _grandiflora_, etc.
_Cyclamen europæum_ (Alpine Violet); the tubers are poisonous.
Order 2. =Myrsinaceæ.= Trees or shrubs; evergreen, tropical
Primulaceæ with fleshy fruits and few seeds, embedded in the
placenta. The leaves are nearly always dotted with yellow
glands (schizogenous resin-receptacles).--550 species;
especially Am.--ORNAMENTAL PLANTS: _Ardisia crenulata_ (W.
Ind.); other genera: _Clavija_, _Maesa_, _Theophrasta_ (barren
sepal-stamens), _Myrsine_, _Jacquinia_ (barren sepal-stamens),
etc.--_Ægiceras_, allied to this order, comprises arborescent
plants, often growing with _Rhizophora_ in tropical forests,
along the shore. The embryo germinates while still in the fruit.
Order 3. =Plumbaginaceæ.= This order has a position of the stamens
similar to that in Primulaceæ (S5, P5, A0 + 5, G5), but it differs
from these in the flower, which has generally a _membranous_, dry,
thin, coloured, folded, almost entire calyx and an _almost entirely
polypetalous corolla_, which, as a rule, has twisted æstivation and is
_only united_ with the stamens _at its base_; but more especially it
differs in the ovary, which bears 5 _free_ or almost free _styles_ and
only 1 _basal_ ovule with a _long_, twisted funicle (the placenta of
the Primulaceæ is here so much reduced that it bears only 1 ovule).
The fruit is a _nut_ or _capsule_. The radicle is turned outwards.
Endosperm mealy.--To this order belong herbs or under-shrubs, which
are especially natives of the sea-coast and of salt-steppes; they also
resemble the Primulaceæ in the scattered, undivided, entire leaves
(without stipules), often in rosettes, and the inflorescence borne
on a long stalk. In opposition to the Primulaceæ, the _bracteoles
are typically present, and hence the branching is generally cymose_
(scorpioid).
_Armeria_ (Thrift) has a round _capitulum_, composed of closely-packed
dichasia, surrounded at its base by an involucre with peculiar
prolongations, directed downwards, and united into a sheath protecting
the intercalary zone of growth. The pericarp is finally ruptured at
the base, and drops off like a hood.--In _Statice_ (Sea-lavender), the
unipared scorpioid cymes are prolonged and collected into panicle-like
inflorescences.--~_Plumbago_ is the genus which approaches nearest to
the Primulaceæ, and differs most from the characters given above. It
has capitate or spike-like inflorescences, a salver-shaped corolla, and
the stamens are not attached to the corolla. The style is only divided
at the extremity; the calyx is not membranous, but is covered with
sticky, glandular hairs.~
250 species; chiefly in the Mediterranean and about the Caspian
Sea, on salt-steppes and beaches. Some are Tropical; a few are
ornamental plants.
B. Tetracyclicæ.
a. Tetracyclicæ with hypogynous flowers.