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Ch. VIII.] FLOWERS FERTILIZED BY BIRDs. 129

hanging downwards, like an inverted candelabrum. From the centre of the circle of flowers is suspended a number of pitcher-like vessels, which, when the flowers expand, } in February and March, are filled with a sweetish liquid. This liquid attracts insects, and the insects numerous

z- FLOWER of MARCGRAVIA NEPENTHOIDEs.

insectivorous birds, including the species I have menof tioned and many kinds of humming-birds. The flowers are so disposed, with the stamens hanging downwards, that the birds, to get at the pitchers, must brush against y them, and thus convey the pollen from one plant to another. A second species of Marcgravia that I found in the woods around Santo Domingo has the pitchers * placed close to the pedicels of the flowers, so that the o birds must approach them from above; and in this species the flowers are turned upwards, and the pollen is brushed off by the breasts of the birds. In temperate

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- - s 130 THE NATURALIST IN NICARAGUA.. [Ch. VIII.

latitudes we find many flowers fertilised by insects
attracted by honey-bearing nectaries; and in tropical
America not only bees, moths, and other large insects

carry the pollen from one flower to another, but many
flowers, like the Marcgravia, are specially adapted to .

secure the aid of small birds, particularly humming-birds,
for this purpose. Amongst these, the “palosabre,” a
species of Erythrina, a small tree, bearing red flowers,

FLOWER OF PALOSABRE.

that grew in this valley, near the brook, often drew my

attention. The tree blooms in February, and is at the

time leafless, so that the large red flowers are seen from
a great distance. Each flower consists of a single long,
rather fleshy petal, doubled over, flattened, and closed,
excepting a small opening on one edge, where the
stamens protrude. Only minute insects can find access
to the flower, which secretes at the base a honey-like
fluid. Two long-billed humming-birds frequent it ; one
(Heliomaster pallidiceps, Gould), which I have already
mentioned, is rather rare; the other (Phaethornis longi-
rostris, De Latt.) might be seen at any time when the
tree was in bloom, by watching near it for a few minutes.
It is mottled brown above, pale below, and the two
middle tail feathers are much longer than the others.
The bill is very long and curved, enabling the bird easily

to probe the long flower, and with its extensile cleft

tongue pick up the minute insects from the bottom of

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the tube, where they are caught as if in a trap, their
only way of exit being closed by the bill of the bird.
Whilst the bird is probing the flower, the pollen of the
stamens is rubbed in to the lower part of its head, and
thus carried from one flower to fecundate another. . The
bottom of the flower is covered externally with a thick,
fleshy calyx—an effectual guard against the attempts of
bees or wasps to break through to get at the honey.
Humming-birds feed on minute insects, and the honey
would only be wasted if larger ones could gain access
to it, but in the flower of the palosabre this contingency
is simply and completely guarded against.
Many flowers have contrivances for preventing useless
insects from obtaining access to the nectaries. Amongst
our English flowers there are scores of interesting
examples, and I shall describe the fertilisation of one,
the common foxglove, on account of the exceeding sim-
plicity with which this object is effected, and to draw the
attention of all lovers of nature to this other branch of a
subject on which the labours of Darwin and other natu-
ralists have of late years thrown a flood of light. The
pollen of the foxglove (Digitalis purpurea) is carried from
one flower to another by the humble bee, who, far more
than the hive bee, that “improves each shining hour,”
deserves to be considered the type of steady, persevering
industry. It improves not only the hours of Sunshine,
but those of cloud, and even rain; and, long before the
honey-bee has ventured from its door, is at work bustling
from flower to flower, its steady hum changing to an
important Squeak as it rifles the blossoms of their sweets.

The racemes of purple bells held up by the foxglove are

methodically visited by it, commencing at the bottom

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flower, and ascending step by step to the highest. The four stamens and the pistil of the foxglove are laid closely against the upper side of the flower. First a stamen on one side opens its anthers and exposes its pollen. The humble-bee, as it bustles in, brushes this off. Then another stamen exposes its pollen on the other side, then another and another; but not till all the pollen has been brushed off does the cleft-end of the pistil open, and expose its viscid stigma. The humblebee brushes off the pollen into its hairy coat from the upper flowers of one raceme and carries it direct to the lowest flowers of another, where the viscid stigmas are open and ready to receive it. If the humble-bee went first to the upper flowers of the spike and proceeded downwards, the whole economy of this plant to procure cross fertilisation would be upset.* The open flower of the foxglove hangs downwards. The lower part, or dilated opening of the tube, is turned outwards, and has scattered stiff hairs distributed over its inner surface; above these the inside of the flower hangs almost perpendicularly, and is smooth and pearly. The large humblebee bustles in with the greatest ease, and uses these hairs as footholds whilst he is sucking the honey; but the smaller bees are impeded by them, and when, having at last struggled through them, they reach the pearly, slippery precipice above, they are completely baffled. I passed the autumn

* Darwin mentions having seen humble bees visiting the flowering spikes of the Spiranthes autumnalis (ladies’ tresses), and notices that they always commenced with the bottom flowers, and crawling ... spirally up sucked one flower after the other, and shows how this proceeding ensures the cross fertilisation of different plants.-‘‘ Ferbilisation of Orchids,” 127.

Ch. VIII. SPIDERS THE PREY OF WASPS. 133

of 1857 in North Wales, where the foxglove was very abundant, and watched the flowers throughout the season, but only once saw a small bee reach the nectary, though many were seen trying in vain to do so. Great attention has of late years been paid by naturalists to the wonderful contrivances amongst flowers to secure cross fertilisation; but the structure of many cannot, I believe, be understood, unless we take into consideration not only the beautiful adaptations for securing the services of the proper insect or bird, but also the contrivances for preventing insects that would not be useful from obtaining access to the nectar. Thus the immense length of the Angraecum Sesquipedale of Madagascar might, perhaps, have been more easily explained by Mr. Wallace, if this important purpose had been

taken into account.

The tramway in some parts was on raised ground, in others excavated in the bank side. In the cuttings the nearly perpendicular clay slopes were frequented by many kinds of wasps that excavated round holes of the diameter of their own bodies, and stored them with stingparalysed spiders, grasshoppers, or horse-flies. Amongst these they lay their eggs, and the white grubs that issue therefrom feed on the poor prisoners. I one day Saw a small black and yellow banded wasp (Pompilus polistoides) hunting for spiders; it approached a web where a spider was stationed in the centre, made a dart towards it—apparently a feint to frighten the spider clear of its web; at

any rate it had that effect, for it fell to the ground, and

was immediately seized by the wasp, who stung it, then ran quickly backwards, dragging the spider after it, up a

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