BEES IN RELATION TO FLOWERS.
Connection of Plant-life and Insect-life--Reproduction of Flowers--
Intervention of Insects--Hermaphrodite Flowers--Cross-fertilisation
--Cucumbers, Melons, &c.--Poplars--Firs--Epilobium or Willow Herb--
Cincerarias--Darwin's Experiments--Nasturtium--Foxglove--Figwort--
Salvia--Heath--Strawberry, Raspberry, and Blackberry--Apple and Pear
--Altruism of Bees.
The connection between insects and the plant-world, and the mutual
benefits they render, have long been known to man. While the one
kingdom is almost entirely dependent on the other for sustenance,
and this, not only as regards food, but for dwelling-places also:
the organic, but (so far as we can judge) inanimate, one of the two,
requires the aid of the animate for the continued reproduction of many
of its members.
It would lead us too far from the subject of this book to enter at
all fully into the question of the complete interaction of plant-life
and insect-life. In dealing with the relations of bees to flowers we
shall, therefore, confine our remarks almost entirely to the important
part played by these creatures in the reproduction of certain kinds of
plants.
It may, perhaps, be necessary, previously to entering on this subject,
to say that in flowers we have organs analogous to, though widely
differing from, those indicative of sex in the animal world. The
functions, at least, are the same; and the combined action of the
two sets is essential to the propagation of the race by seed. Unless
pollen from the anthers is conveyed to the pistil, and, germinating
there, imparts to the ovules vivifying nourishment, no seed will come
to perfection, or will be capable of growing. While most flowers are
hermaphrodite, _i.e._ produce both stamens (or anther-bearers) and
pistils, it happens, in not a few instances, that certain flowers
have anthers, and no pistils: while others, on the same plant, have
pistils, but no anthers. Again, the antheriferous and pistiliferous
flowers, in certain species, are found on different individual plants,
so that, unless some agency were provided for the transference of the
pollen, these species would inevitably die out. Now, the two means
for this conveyance are the wind and insects. It is evident that the
former can have only a very limited action, and would need for its
effective service a great abundance of any particular flower, lest
the fructifying grains should become the mere sport of the breezes,
and fail to reach their all-important goal, and accomplish their
all-needful function.
Moreover, in many cases, the position of the anthers in the flower
entirely excludes the possibility of any currents of air assisting
in the carrying of the pollen-dust to the pistil of the same or of
different flowers. Hence there is a necessity for the intervention
of insects; and that they may be induced to visit such flowers, and
unconsciously effect the essential operation of fertilising them,
nectar is secreted near the base of the stamens or the ovary, or in
some position which will involve, in the gathering of it, the brushing
off and conveying away of some of the pollen-grains. It is, indeed,
a remarkable fact that fragrance and honey-bearing are scarcely ever
associated with plants which can easily be wind-fertilised. Such
flowers are, also, for the most part, inconspicuous; while those which
need the agency of insects to aid in their reproduction are bright in
colour, sweet in perfume, and more or less prolific in honey.
It must not be supposed, however, that even the hermaphrodite, or
double-sexed, flowers are independent of the visits of bees and other
insects. In all of them cross-fertilisation, as Darwin has abundantly
proved,[10] is a most important factor in the continued vitality of any
species, and cross-breeding gives an immense advantage in "the struggle
for existence," where the conditions of life are not wholly favourable.
Indeed, in many instances, special provision has been made by the
Creator against self-fertilisation: in some cases, by the anthers and
pistil coming to maturity, in the same flower, at different times; in
others, by the placing of the stamens in such a position relatively
to the stigma (or top of the pistil) that it is not possible for the
pollen-grains of the one set of organs to fall on the surface of the
other. It cannot but be interesting to give examples of these various
facts, and so to show the marvellous and necessary connection between
the two kingdoms of nature.
[Footnote 10: For full and most interesting information on this point,
vide _Cross and Self-Fertilisation of Plants_, by Charles Darwin.
Murray.]
Firstly, then, as well-known instances of pistil-bearing and
stamen-bearing flowers occurring separately on the same plant, we may
mention cucumbers, melons, marrows, _et hoc genus omne_. Now, when
these vegetables are grown under glass, whether in greenhouses or
in pits, to which bees and other insects have little or no access,
gardeners find it necessary themselves to apply the pollen-bearing
portions of the one kind of flower to the pistil of the other. If this
is neglected to be done, the fruit makes no progress, turns yellow, and
dies. Where, however, the plants are grown in the open air, or are not
so shut up as to exclude insects, they will be fertilised without the
intervention of man; for bees of various kinds will certainly visit the
flowers, and carry the life-giving dust where it is needed. In fact,
we believe it might be asserted with confidence, that in all plants,
where this separation of, what we may call, the sexes takes place, the
flowers possess special attractiveness to the tenants of our hives; and
it is well that this is the case, otherwise the continued existence of
such plants would be seriously endangered.
As examples of diœcious genera, or those having pollen-bearing flowers
on one plant and pistiliferous flowers on another, we may note the
willows, the poplars, and the firs; and it is remarkable that these all
are special favourites with bees. In the early spring, when breeding
has been going on in the hives, and when the demands of the advancing
larvæ require considerable supplies of pollen, the catkins of the
willow are abundantly visited, and the diffusion of their fertilising
powder is thus greatly promoted. The same may be said about the poplar,
and, in all probability, the gathering of propolis from trees of
the fir-tribe makes the bee the unconscious, but useful, instrument
of carrying pollen from the catkins to the cones, though, from the
abundance of the powder, and the openness of the scales of the cones r
the wind is a sufficiently effective agent for its conveyance in this
order of trees.
[Illustration: Fig. 70.--Epilobium Angustifolium. (Young bloom.)]
[Illustration: Fig. 71.--Epilobium Angustifolium. (Old bloom.)]
Passing next to cases in which the stamens and pistils of the
same flower come to maturity at different times, so as to make
cross-breeding a necessity, we may mention first some plants in which
the pollen ripens before the stigma is ready to receive it. We have
such a condition of things in the _willow-herb_, or _epilobium tribe_.
The pretty pink blossoms of a large variety of this genus are to be
found, in summer, along the banks of brooks and running ditches. We
will confine our remarks to the species distinguished by its narrow
leaves, and hence named _angustifolium_. When the flower has fully
opened, the eight stamens spread out, and their anthers shed the
pollen. Bees visit the blossoms, and getting dusted with the grains,
carry these away to other flowers of the same kind. And here, in
passing, we may recall the fact of bees keeping to one species of plant
during the whole of any one journey from the hive. The importance
of this can be now better appreciated, when its influence on the
fructification of blossoms is observed. But to return, the pistil of
the willow-herb remains, till the stamens have withered, curved round
out of the way, and unable to receive any of their pollen. Then, after
they are dead, it comes into such a position that it can take what
pollen may be brought to it from younger flowers. For the conveyance of
this it is dependent chiefly on bees, who do not fail to carry enough
for the required purpose. In this way each blossom, by the agency of
these insects, both gives and gets what is necessary for the continued
life of the species; and without these unconsciously conferred benefits
from insect life, no seeds of this kind of _epilobium_ would mature.
Another instance, equally interesting, is seen in the well-known
_cineraria_ tribe. The plants of this genus belong to the _composite_
order, in which what is usually called the blossom, consists of many
flowers, grouped together on one head. In the example before us, there
are nearly 200 thus aggregated. These florets separately open at
different times, those of the outer circles coming before those nearer
the centre. The pollen-tube of each is formed by five anthers, fastened
together at their edges, and discharging their pollen into the space
between them. At the lower part of this inclosure the pistil is
growing, but is not in a condition to receive usefully the fertilising
powder. It, however, as it advances, sweeps out, and carries up with
it, the pollen-grains, so that they may be conveyed to other florets of
the same or other blossoms, to effect their vitalising work. At length
the pistil, with its brush on its summit, comes into view, but, even
yet, is not sufficiently developed for fertilisation. In due course,
however, the upper end splits, and exposes the surface of the stigma
ready for the pollen, which must be brought from some other floret, and
probably from some other blossom. Thus cross-breeding is effectually
secured.
[Illustration: Fig. 72.--Cineraria. (Magnified.)]
Another point for attaining this end is worthy of remark. The outer
ring of florets is distinguished by long, coloured petals, which make
up, in common parlance, the flower of the cineraria. These serve to
render the composite head conspicuous, and attractive to insects. Some
varieties, moreover, emit fragrant odours, and thus present further
inducements for visitation. It is remarkable that, in these florets of
the outer edge, the gay-coloured petals are developed at the expense of
the anthers. Consequently, they produce no pollen, and their pistils
have no brushes, as there would be no office for them to perform.
The bright rays have accomplished their own special purpose, and the
florets may well depend on others for pollen.
Now, as to the great importance of cross-fertilisation in this species,
we may quote the experiments made by Dr. Darwin.[11] He says: "Two
purple-flowered varieties (of cineraria) were placed under a net in
the greenhouse, and four corymbs (or bunches of flowers) on each
were repeatedly brushed with flowers from the other plant, so that
their stigmas were well covered with each other's pollen. Two of the
eight corymbs thus treated produced very few seeds, but the other six
produced on an average 41.3 seeds per corymb, and these germinated
well. The stigmas on four other corymbs on both plants were well
smeared with pollen from the flowers on their own corymbs; these eight
corymbs produced altogether ten extremely poor seeds, which proved
incapable of germinating. I examined many flowers on both plants, and
found the stigmas spontaneously covered with pollen; but they produced
not a single seed. These plants were afterwards left uncovered in the
same house, where many other cinerarias were in flower; and the flowers
were frequently visited by bees. They then produced plenty of seed,
but one of the two plants less than the other, as this species shows
some tendency to be diœcious.
[Footnote 11: See _Cross and Self-Fertilisation of Plants_, p. 335.]
"The trial was repeated on another variety with white petals tipped
with red. Many stigmas on two corymbs were covered with pollen from
the foregoing purple variety, and these produced eleven and twenty-two
seeds, which germinated well. A large number of the stigmas on several
of the other corymbs were repeatedly smeared with pollen from their
own corymb; but they yielded only five very poor seeds, which were
incapable of germination. Therefore the above three plants, belonging
to two varieties, though growing vigorously and fertile with pollen
from either of the other two plants, were utterly sterile with pollen
from other flowers on the same plant."
[Illustration: Fig. 73.--Tropœolum Majus. (Young bloom.)]
[Illustration: Fig. 74.--Tropœolum Majus. (Old bloom.)]
A condition similar to that described in the cineraria is found in the
nasturtium (_Tropœolum majus_). In the young blossom may be observed
the five stamens fully developed, while the stigma remains quite out
of their reach. Later, when all the pollen is discharged from the
anthers, the pistil throws up its style and stigma, now ready for
fertilisation, which must be effected by the transfer of pollen from
some other blossom of the same or another plant of the species. This
transfer is effected, usually, by the bees.
Another example of this non-coincidence in the times of development of
the stamens and pistil is found in the foxglove (_Digitalis purpurea_),
but the fertilisation is effected by the larger humble-bees. The
two upper and longer stamens shed their pollen before the two
lower and shorter ones. This arrangement partly avoids the risk of
self-fertilisation, while their position, which changes just when the
anthers are ripe, enables them to smear the under side of any entering
bee; while they also shed their pollen abundantly on the thickly-set
hairs lining the mouth of the corolla. A second use is served by these
hairs, viz., that of obstructing the entrance of the smaller kinds of
bees, which could not so effectually fertilise the ovules. The larger
sorts, in their raids upon the nectar, carry pollen from flower to
flower, thus in the best manner bringing about the most desirable
result of cross-breeding.
Passing now to plants in which the pistil develops earlier than the
stamens, we may note the knotted figwort (_Scrophularia nodosa_). On
making a section of a recently opened flower, the style, with its
stigma, may be observed protruding just beyond the lip of the corolla,
while the stamens are hiding away, as it were, in a little pouch
below the entrance of the blossom. When fertilisation by pollen from
another flower has taken place, the pistil droops and withers; while
the anthers grow upwards to the mouth of the corolla, and present their
nectar to the honey-seekers, for conveyance to other flowers of the
species.
[Illustration: Fig. 75.--Section of Scrophularia Nodosa.]
[Illustration: Fig. 76.--Scrophularia Nodosa. (Young bloom.)]
[Illustration: Fig. 77.--Scrophularia Nodosa. (Old bloom.)]
In the common sage (_Salvia officinalis_) we find a very remarkable
contrivance, by means of which the anthers, through a sort of
hinge-like connective, are brought down on the back of a bee entering
the flower. The pollen thus discharged is carried by the insect to
other blossoms, in which the place of the withered stamens has been
occupied by the stigma now ready to receive the grains. Thus again
inter-breeding is secured.
[Illustration: Fig. 78.--Salvia Officinalis. (New bloom.)]
[Illustration: Fig. 79.--Salvia Officinalis. (Old bloom.)]
[Illustration: Fig. 80.--a. Erica Tetralix. b. Anther of Tetralix.]
The next figure represents the very curious arrangement of the stamens
in the _Erica tetralix_, or common heath. These, eight in number, are
seen standing round the style, at about half its length. Each is held
by a long filament (only one of which is shown in the figure), and is
armed with a horn-like process. When the anthers are ripe, the pollen
would escape from openings in their sides, were it not that the little
slits abut on each other. When, however, a bee visits the flower,
and thrusts up her proboscis, this strikes against one of the little
horns, and pulls apart its anther from the rest. Pollen then drops on
the bee's head, to be carried by it to other blossoms, which, while
receiving a portion brought to them, in their turn give the bee a
supply to carry to other flowers. It is a very salutary thing for the
propagation of the heath that bees have such a strong liking for its
nectar, and are thus induced to perform, albeit unconsciously, the
process of fertilisation.
[Illustration: Fig. 81.--Section of Strawberry Bloom.]
In the strawberry the stigmas are ripe long before the pollen is ready;
and hence we understand why the Creator has arranged that the nectar
of these blossoms should be so attractive to the bees, whose visits
are so necessary for the development of the fruit. When fertilisation
takes place, growth proceeds in the ordinary manner, and with results
so satisfactory to mankind. Where pollen fails to fall on any of the
multitudinous stigmas, we have a shrunken, hard, greenish mass. Any
dish of strawberries will show where this has happened. It is said that
to produce one perfect specimen of the fruit, from 100 to 300 separate
fertilisations must be effected.
In the raspberry and blackberry again, each drupel, or little fleshy
portion, of which very many make up one so-called berry, has had its
own stigma, which an insect has visited; and hence again, we understand
how it is that the flowers have been so largely endowed with nectar, as
to entice the bees most freely to visit them.
[Illustration: Fig. 82.--Section of Apple Bloom.]
In apple and pear blossoms we have other instances of the stigmas
coming to maturity before the anthers; and, therefore, they require
the intervention of bees for their fertilisation. Peaches, apricots,
nectarines, plums, greengages, and, we might almost venture to
assert, all our choicest and most valuable fruits, are dependent for
their perfection upon the busy searchers after honey; and many a
market-gardener would greatly increase his chances of good crops of
fruit, were he to maintain a few stocks of bees in his orchards, and
allow access for the active workers to his trees blossoming under
glass-houses.
From the vegetable world we might adduce many other evidences of the
marvellous interdependence of the two great kingdoms of organic nature.
Enough, however, has been said to illustrate this point, and we trust
that some of our readers may be led to further investigation in this
field, which opens up such wonders, and such pleasurable surprises, for
all who care to trace evidences of the Creator's infinite resources,
wisdom, and care for all that He has made.
Everywhere, also, on earth may be seen at work the grand law of
self-sacrifice for others' needs. Very many facts which we have
detailed in the natural history of bees, illustrate this most
thoroughly. We may, indeed, say that the life of a worker, who will
neither have progeny of her own, nor see many of the race for whom
she spends her powers, is one continued offering of herself for the
welfare of the community. As the Latin poet says, _Sic vos non vobis,
mellificatis apes_; and thus these unselfish toilers, beside teaching
us many another lesson, seem to foreshadow, and to lead our thoughts
to, the infinite gift of Him "who gave Himself for us" that we in and
through Him might have life.
God has written tokens of His wisdom and love around us everywhere.
None who reverently observe any of His works can fail to see His
attributes embodied throughout all nature.