In Broom there is an explosive mechanism; the pressure of the insect visitor on the keel of the corolla causes a sudden release of the stamens and the scattering of a cloud of pollen over its body.
6.
Lepidopterid flowers, visited chiefly by Lepidoptera, which are able to reach the nectar concealed in deep, narrow tubes or spurs by means of their long slender proboscis. Such are: (a) Butterfly-flowers, usually red in colour, as Dianthus carthusianorum; (b) Moth-flowers, white or whitish, as honeysuckle (Lonicera periclymenum).
7.
Fly flowers, chiefly visited by Diptera, and including very different types:—
a.
Nauseous flowers, dull and yellowish and dark purple in colour and often spotted, with a smell attractive to carrion flies and dung flies, e.g. species of Saxifraga.
b.
Pitfall flowers such as Asarum, Aristolochia and Arum maculatum, when the insect is caught and detained until pollination is effected (fig. 10).
c.
Pinch-trap flowers, as in the family Asclepiadaceae, where the proboscis, claw or bristle of the insect is caught in the clip to which the pairs of pollinia are attached. Bees, wasps and larger insects serve as pollinating agents.
d.
Deceptive flowers such as Parnassia, where the conspicuous coronet of glistening yellow balls suggests a plentiful supply of nectar drops (fig. 11).
e.
Hoverfly flowers, small flowers which are beautifully coloured with radiating streaks pointing to a sharply-defined centre in which is the nectar, as in Veronica chamaedrys (fig. 12).
Fig. 10.—Spadix of Arummaculatum from which the
greater part of the spathe has
been cut away.
p, Pistillate, s, staminate
flowers; h, sterile flowers forming
a circlet of stiff hairs closing
the mouth of the chamber
formed by the lower part of
the spathe.
(From Vines’s Text Book of Botany, by permission.)
Fig. 12.—Flower of Veronica.
k, Calyx. u, u, u, The three lobes of the lower lip of the rotate corolla. o, The upper lip. s, s, The two stamens. n, The stigma.
Fig. 11.—Grass of Parnassus (Parnassia palustris).
1. One of the scales which form the coronet in the flower, enlarged.
Literature.—Joseph Gottlieb Kölreuter[1] (d. 1806) was the first
to study the pollination of flowers and to draw attention to the
necessity of insect visits in many cases; he
gave a clear account of cross-pollination
by insect aid. He was followed by Christian
Konrad Sprengel, whose work Das entdeckteGeheimniss der Natur im Bau und in derBefruchtung der Blumen (Berlin, 1793),
contains a description of floral adaptations
to insect visits in nearly 500 species of
plants. Sprengel came very near to
appreciating the meaning of cross-pollination
in the life of plants when he states
that “it seems that Nature is unwilling
that any flower should be fertilized by its
own pollen.” In 1799 an Englishman,
Thomas Andrew Knight, after experiments
on the cross-fertilization of cultivated
plants, formulated the conclusion that no
plant fertilizes itself through many generations.
Sprengel’s work, which had been
almost forgotten, was taken up again by
Charles Darwin, who concluded that no
organic being can fertilize itself through
an unlimited number of generations; but
a cross with other individuals is occasionally—perhaps
at very long
intervals—indispensable. Darwin’s works on dimorphic flowers and the fertilization
of orchids gave powerful support to this statement. The
study of the fertilization, or as it is now generally called “pollination,”
of flowers, was continued by Darwin and taken up by other
workers, notably Friedrich Hildebrand, Federico Delpino and the
brothers Fritz and Hermann Müller. Hermann Müller’s work on
The Fertilization of Flowers by Insects and their Reciprocal Adaptations
(1873), followed by subsequent works on the same lines, brought
together a great number of observations on floral mechanisms and
their relation to insect-visits. Müller also suggested a modification
of the Knight-Darwin law, which had left unexplained the numerous
instances of continued successful self-pollination, and restated
it on these terms: “Whenever offspring resulting from crossing
comes into serious conflict with offspring resulting from
self-fertilization, the former is victorious. Only where there is no
such struggle for existence does self-fertilization often prove satisfactory
for many generations.” An increasing number of workers
in this field of plant biology in England, on the Continent and in
America has produced a great mass of observations, which have
recently been brought together in Dr Paul Knuth’s classic work,
Handbook of Flower Pollination, an English translation of which
has been published (1908) by the Clarendon Press.
POLLIO, GAIUS ASINIUS (76 B.C.–A.D. 5; according to some,
75 B.C.–A.D. 4), Roman orator, poet and historian. In 54 he
impeached unsuccessfully C. Porcius Cato, who in his tribunate
(56) had acted as the tool of the triumvirs. In the civil war
between Caesar and Pompey Pollio sided with Caesar, was
present at the battle of Pharsalus (48), and commanded against
Sextus Pompeius in Spain, where he was at the time of Caesar’s
assassination. He subsequently threw in his lot with M.
Antonius. In the division of the provinces, Gaul fell to Antony,
who entrusted Pollio with the administration of Gallia
Transpadana. In superintending the distribution of the Mantuan
territory amongst the veterans, he used his influence to save
from confiscation the property of the poet Virgil. In 40 he
helped to arrange the peace of Brundisium by which Octavian
(Augustus) and Antonius were for a time reconciled. In the
same year Pollio entered upon his consulship, which had been
promised him in 43. It was at this time that Virgil addressed
the famous fourth eclogue to him. Next year Pollio conducted
a successful campaign against the Parthini, an Illyrian people
who adhered to Brutus, and celebrated a triumph on the 25th
of October. The eighth eclogue of Virgil was addressed to
Pollio while engaged in this campaign. From the spoils of the
war he constructed the first public library at Rome, in the
Atrium Libertatis, also erected by him (Pliny, Nat. hist. xxxv.
10), which he adorned with statues of the most celebrated
↑Vorläufige Nachricht von einigen das Geschlecht der Pflanzenbetreffenden Versuchen und Beobachtungen, 3, 4, 6 (Leipzig, 1761).
