CHAPTER IV

SOME INTER-RELATIONS OF PLANTS AND ANIMALS

The most important and fundamental difference between the animal and plant worlds is this: plants possess the power of manufacturing their food out of the inorganic materials of which it is composed, while animals cannot do this. Give an ordinary plant access to water with a pinch of mineral salts in it, to the air, and to sunlight, and by the agency of chlorophyll--the green colouring-matter of the leaves--the miracle will be accomplished, and dead materials transformed into living substance. Animals, on the other hand, are dependent for their food-supply on organic material--that is, on either plant or animal substances; and since they cannot live by taking in each other’s washing--in other words, by eating each other--it follows that the animal world is dependent on the plant world for its continued existence. A porpoise may live on herrings, herrings on small fry, fry in turn on minuter organisms, and so on down the scale; but their ultimate source of food is the tiny Algæ which swarm in the water--the _Plankton_ in Hensen’s original sense--which, alone in this chain, can build up their bodies out of the sea and air. That these minute plants can sustain the enormous drain upon them due to their use as a food-supply by myriads of larger organisms is due to their vast numbers and rapid increase. Sea-water favourable for plankton life may contain several millions of individuals in every litre (about 1-3/4 pints); while as a fair estimate for the seas which surround our own islands “at least one” organism for every drop has been suggested.[6]

In the great abysses of the ocean, where vegetable life is absent, the strange creatures which live there in utter darkness prey upon others, and they again on others which belong to lesser depths, the ultimate source of life being again the minute surface organisms which, possessing chlorophyll, can make organic out of inorganic substances by the energy obtained from sunlight. Thus only is life made possible in

the green hells of the sea Where fallen skies and evil hues and eyeless creatures be.

On the land, the dependence of animals on plants is in large measure direct, as the supply of vegetable food is abundant and widespread. The largest land animals are all vegetable feeders; so are the majority of our own native mammals, and in a great measure our birds; while most of the creatures upon which the flesh-eating animals prey are themselves vegetable feeders. The distribution of land animals over the globe is thus dependent in large measure on the distribution of plants. On account of the profusion and variety of plant life, and the fact that most vegetable feeders can thrive on various sorts of plants, few animals are restricted in their range by the presence or absence of any particular species or genus, but complete dependence of this sort is by no means unknown. The larvæ of some Butterflies, for instance, eat the leaves of one plant only; the Peacock (_Vanessa io_) and the Small Tortoiseshell (_V. urticæ_) are cases in point. The caterpillars of both these species feed exclusively on the Common Nettle (_Urtica dioica_). Should the efforts of farmers and gardeners succeed in exterminating this unwelcome plant, these two butterflies would disappear from the Earth. Sometimes absolute mutual dependence is found on both the animal and vegetable sides. The American _Yucca filamentosa_, often grown in our gardens, depends solely on the little moth _Pronuba yuccasella_ for its pollination, just as the insect is absolutely dependent on the plant (see p. 80), and other species of Yucca have each its particular dependent moth, which feeds on no other plant, and whose flowers are pollinated by no other.

Apart from such special cases, the general dependence of animals upon plants is obvious, and is by no means confined to food-supply. Animals of all grades, from human beings to Caddis Worms, construct houses of vegetable materials; trees are the chosen home of large sections of our fauna, and the herbs of the field are the world for millions of tiny beings.

There’s never a leaf or a blade too mean To be some happy creature’s palace.

Turning to the other side of the picture, no such general dependence of the plant world upon the animal world is found, but the inter-relations of the two are many and varied, and in the absence of animals of one kind or another whole groups of plants would become extinct. The cases where plants derive their food-supply wholly from animals are indeed rare, save near the bottom of the vegetable scale, and most of such parasites are minute; one of the most noticeable in our own country is the fungus _Cordyceps militaris_, which may be found growing on the dead bodies of larvæ or pupæ which it has killed--a little scarlet, club-shaped plant, about an inch in height. But some of the most highly organized plants obtain _portions_ of their food-supply from animal sources. Mention has already been made of the Sundews (_Drosera_), Butterworts (_Pinguicula_), and Bladderworts (_Utricularia_), which capture live insects, etc., by means of sensitive organs (as in the first two cases) or ingenious traps (as in the last), and subsequently digest them, and they will be dealt with later on (p. 186). Then there is the Venus’ Fly-trap (_Dionæa_) and the well-known Pitcher Plants (_Nepenthes_), which actively, as in the former case, or passively, as in the latter, catch insects and digest them, by means of leaves modified in very extraordinary ways. In all these instances the advantage lies entirely on the side of the plant, just as in the case of most of the plant-eating animals the advantage is wholly with the animal. But in a large number of instances--many of them of a most interesting nature--the inter-relations are such as to benefit both the actors, each obtaining from the other what is useful to it. One of the most conspicuous and widespread relationships of this kind is that prevailing between flowers and insects, the insect receiving food in the form of nectar, and at the same time carrying pollen from flower to flower, without which transfer no fertile seed would be formed. To this interchange of favours we shall return later (p. 81); meanwhile, it will be well to consider a few of the cases in which the relationship between plant and animal is continuous and more intimate, the two living in very close relations to each other: to such cases the term _symbiosis_ or “living together” is applied by naturalists. The relations existing between certain trees and some species of ant are of high interest, and illustrate well this phase of life. The Candelabra Tree (_Cecropia peltata_) of the South American forests is liable to attack by leaf-cutting ants (_Œcodoma_), which climb trees and bite off thousands of leaves; these they cut up on the ground and carry to their nests, where they form a basis for the growth of certain small fungi which are a favourite food of the ants (compare the cultivation of mushrooms as practised by gardeners). The Candelabra Tree protects itself from these ravages by forming an alliance with another kind of ant (_Azteca_). Along the hollow stems are little pits through which the ants easily bore, and reach the convenient houses within, where they live and bring up their young. At the base of the leaf-stalks, where the greatest danger lies from the leaf-cutting ants, little tufts of hairs are situated, among which are small white masses of nutritious material much liked by the ants, and collected by them and stored within their houses. So that these desirable trees are swarming with Aztec ants, fierce little creatures--“it is one of the most bellicose ants that I know, and its sting is most irritating,” writes Kerner--which congregate especially at the leaf-stalks, the point of attack of the leaf-cutters. The advantages of these arrangements to both the trees and the Aztec ants are obvious.

A very remarkable instance of a different kind is supplied by the relations existing between the American species of _Yucca_ and the small white-winged moths of the genus _Pronuba_. The following succinct account is given by Professor G. H. Carpenter:[7] “The female of these moths has not only the palps of the first maxillæ developed, but the region of the maxillæ (palpiger) whence they spring produced into a pair of long, flexible, hairy processes. By means of these she collects from the anthers pollen, which she deliberately carries to the stigma to ensure fertilization. With her piercing ovipositor--a most abnormal development among moths--she bores through the tissue of the pistil, and by means of the flexible egg-tube, protrusible beyond the ovipositor, lays her eggs close to the ovules of the _Yucca_. The caterpillar when hatched feeds on the growing seed of the plant, which would never develop were it not for the action of the _Pronuba_ moth. This action is most wonderful, in that the moth herself gets no benefit from it. Her food canal is degenerate, and her jaws, useless for sucking, are devoted altogether to the gathering of the pollen; she does not feed in the perfect state. Doubtless her ancestors did so, and were first attracted to the _Yucca_ in search of honey, though the act of pollination is now performed only for the sake of the offspring.”

Among certain lower animals and plants symbiotic connection is often most intimate. For instance, in the body-wall of certain Sea Anemones and Holothurians there are small green cells which were long believed to be part of the animal, and which puzzled naturalists because they contained chlorophyll, that remarkable green substance characteristic of plants, which gives to them the power of forming food out of its raw inorganic materials. These cells are now known to be minute seaweeds (Algæ), which spend their lives in the animal tissues to the benefit of both organisms. The plant, by virtue of its chlorophyll, absorbs carbon dioxide, decomposes it, and gives out oxygen, which is eagerly seized on by the animal. The animal in its turn liberates carbon dioxide, which is required by the plant. Similar relations exist between Algæ and some of the lowly Radiolarians and Foraminifera; in these cases, the animals being very minute, the plant partner plays a more conspicuous rôle. It is noteworthy that these Algæ are quite capable of living and multiplying separately, free from the body of the animals, and the animals also are capable of pursuing an independent existence.

Let us turn now to the relations existing between flowers and insects, which form one of the most picturesque and romantic features of field life, and of which the materials for study and observation are ever at our own doors. What is a flower? A flower is a group of modified leaves set apart for the business of sexual reproduction. The essential parts or _sporophylls_ are of two kinds, which may be borne on the same flower or on separate flowers on one plant, or on separate plants. These are the _stamens_, bearing _pollen grains_ (or _microspores_), from which _male cells_ arise; and _carpels_, which contain _ovules_, each enclosing an _embryo sac_ or _megaspore_, in which is an _ovum_ or _female cell_.

Each stamen consists usually of a slender stalk, the _filament_, bearing an oblong head, the _anther_, which contains four chambers, or pollen sacs, filled with pollen grains; these, when mature, escape into the air by the rupturing of the walls of the chambers.

Each carpel contains in its lower part an ovary, while its upper part presents to the air a surface charged with nutrient substance, the _stigma_, which is often raised on a slender stalk, the _style_.

To secure the production of seed, the first necessary step is _pollination_, or the transfer of pollen from the stamen to the stigma. When this is effected--the means will be considered immediately--and a pollen grain alights on the surface of the stigma, which is usually sticky or hairy to aid its retention there, the pollen grain commences growth, and sends out a slender tube (the _pollen tube_), which pursues its way through the substance of the stigma, down the style, into the ovary, and from its tip a male cell passes out and fuses with the ovum. In most flowers the pollen tube is not called on to make any great effort of growth, the distance between stigma and ovary being very small; but occasionally, as in Crocus and Lily, this may amount to half a foot. The result of this act of fertilization is that the ovum and ovule grow, the former forming eventually the _embryo_, or young plant, the latter the _seed_ in which the embryo is enclosed. In order that fertile seed may be produced it is often necessary, and usually desirable, that the pollen which reaches the stigma should not belong to the same flower, but to a different flower of the same species; _cross-pollination_ being the rule among seed plants, _self-pollination_ the exception. To secure the former, and to avoid the latter, many highly interesting devices are found, materially affecting the structure and development of flowers.

The _essential_ parts of a flower, then, consist of stamens and carpels. Flowers consisting of no other parts but either or both of these are not common, but we may compare, for example, the rarely produced flowers of the Duckweeds (_Lemna_), in which a tiny group of two stamens and a carpel represents one flower, or, according to some views, a group of three flowers. More commonly the flower is much more composite, consisting mostly of four sets of organs, arranged in whorls or rings, or more rarely in close spirals. In the centre is a group of carpels; outside them--in other words, slightly lower on the stem--a ring, or two rings, of stamens, few or many; then a ring of _petals_, forming the _corolla_, usually coloured, leaf-like, and conspicuous; and outside of them a ring of _sepals_, forming the _calyx_, generally green and leaf-like. The main function of the calyx is protective; it encloses the essential organs and guards them till they are mature, when the flower opens and stamen and stigma play their parts. The calyx is usually tough, and often covered with hairs, or with a sticky substance, to keep the flower safe and ward off the attacks of insects or other small devourers. If we turn to the corolla we find a singular variety of size, form, and colour. To account for this, it is necessary to consider the means by which pollen is distributed. There are two chief ways in which pollen is conveyed from flower to flower--by means of the wind, and by means of flying insects. If we examine wind-pollinated flowers, such as Hazel (_Corylus_), Scotch Fir (_Pinus_), or Reed-mace (_Typha_), we note the small size of the flowers and the great abundance of pollen. Compare these with insect-fertilized flowers, such as Buttercup (_Ranunculus_), Flax (_Linum_), Snapdragon (_Antirrhinum_), or one of the Orchids. In these the flowers are much larger owing to the increased size of the petals, which are of brilliant colour and of various shape. Pollen is mostly much reduced in quantity, since insects flying direct from flower to flower afford a far more economical mode of distribution than is offered by the wind. The pollen grains, moreover, are sticky and covered with tiny spines or knobs, to render them more liable to adhere to the body or head of an insect; the pollen grains of wind-fertilized flowers being, on the other hand, smooth, dry, and dust-like. Again, these insect-pollinated flowers usually possess little glands which secrete nectar, the sugary syrup which by digestion in a bee’s body becomes honey. Here, then, is the inter-relation established: the insect helps the plant by carrying its pollen from flower to flower, and in its turn is helped by the provision of delicious food. And what about the showy petals, and the fragrance that so often marks these entomophilous flowers? They are advertisements, designed to catch the attention of the necessary insects as they fly about. Not only does the corolla by its bright colour attract insects, but markings of various shapes and tints upon the petals are generally held to be honey-guides--sign-posts directing the insects to the nectar and to the pollen. These are especially conspicuous in many of the irregular flowers to which reference will be made shortly, in which the insects are encouraged to approach the flowers in a particular way. An example

of such markings, as seen in the genus Erodium, is shown in Fig. 14. It is interesting to note the various ways in which flowers render themselves conspicuous in order to attract insects. In the majority of Seed Plants, such as the Buttercup, Pea, Rose, Foxglove, it is the corolla, formed either of separate petals, as in the first three, or of petals fused together, as in the last, which by its bright colour or colours renders the flower noticeable. In other species the calyx takes on the function of advertisement, the corolla being in comparison insignificant--we may study examples of this in the Anemones, Hellebores, and Marsh Marigold (_Caltha palustris_). It is worth examining this last, to see how its coloured _sepals_ resemble and fulfil the same function as the _petals_ of its cousins the Buttercups. Or, again, sepals and petals may combine in showiness, both sets being brightly coloured in one or more tints--compare the Columbine (_Aquilegia_), Larkspur (_Delphinium_), Milkwort (_Polygala_), and the marvellous flowers of Orchids. In the great group of the Monocotyledons, indeed, to which

the Orchids belong, sepals and petals usually combine in form and colour to form one corolla-like envelope (then called a _perianth_). In many other plant groups--for instance, the _Dipsacaceæ_ (such as the Scabious), _Umbelliferæ_, and _Compositæ_--conspicuousness is obtained by a grouping together of a large number of small flowers. In the Cow Parsnep (_Heracleum Sphondylium_) the outer petal of the marginal flowers of the large umbel is much enlarged, which enhances this effect. In _Astrantia_, an interesting genus of _Umbelliferæ_, the bracts take on the appearance of a ring of large petals, and surround the group of small flowers (Fig. 15). The same thing may be noticed in the outer blossoms of the close flower-head of the Field Scabious (_Knautia arvensis_). In many _Compositæ_ the process is carried still farther; in the Common Daisy (_Bellis perennis_) the outer flowers have each a long strap-shaped expansion of the corolla, which is of a different colour (white) from that of the corollas of the inner flowers, which are yellow. In the Dandelion (_Taraxacum officinale_) all the flowers have a yellow strap-shaped corolla. In the Guelder Rose (_Viburnum Opulus_) the outer flowers are entirely devoted to advertisement, consisting each of a big white corolla, while only the small inner flowers possess stamens and pistil and are capable of producing the brilliant scarlet berries. In a cultivated form of this, commonly called the Snowball Tree, the advertisement flowers only are present, forming a globe of white blossom, and no fruit is produced in consequence. The Dwarf Cornel (_Cornus suecica_), a little Dogwood growing on many Scottish moors, bears what looks like a white flower with a purple centre. On examination it is seen that the four white petal-like structures are really foliage-leaves, which have taken on the duty of advertising the group of small purple blossoms which they enclose (Fig. 16). A similar and very gorgeous effect is produced in several Spurges often seen in greenhouses, such as _Euphorbia fulgens_, _E. splendens_, and _E. punicea_; in these the upper foliage-leaves are large and coloured brilliant scarlet, the flowers which accompany them being quite small. These aggregations of flowers with their flaunting flags are in general an invitation to all comers; the nectar in the blossoms lies open to every hungry insect, and pollination is effected in a rather promiscuous and messy way; not only flying insects--bees, butterflies, beetles, and flies of many sorts--but also ants and other creatures which creep up the stems from the ground, assemble for the feast, and incidentally transfer from flower to flower pollen which may adhere to their bodies.

In a large number of flowers such general feasting is discountenanced, insect traffic is regulated, the visits of insects of little or no service to the plants is discouraged, and special arrangements are made to attract and minister to the needs of those insects whose visits are of most benefit. Except where flowers are borne in clusters, creeping creatures like ants are of no service; for in the course of the journey “by land” from one flower to another, there is a strong probability of any pollen which the insect may be carrying being rubbed off before the next blossom is reached; small flying insects are likewise frequently useless. In many plants the visits of such pedestrians and small fry is very distinctly discouraged. Of different devices which serve this end, the most conspicuous and effective include barriers to the passage of stem-climbers, and devices in the flower preventive of the visits of unwelcome guests. We may take a few instances from among British plants, which the reader may with a little diligence find and study for himself. Several members of the Pink family (_Caryophyllaceæ_) produce a sticky secretion which is a very effectual bar to the passage of small walking animals. In the English Catchfly (_Silene anglica_), Night-flowering Catchfly (_S. noctiflora_) and the Nottingham Catchfly (_S. nutans_), hairs are present all over the leaves and stems, from the tips of which a gummy substance exudes, which is a fatal trap for small insects. Kerner, in his interesting book, “Flowers and their Unbidden Guests,” states that on the sticky stems of the last, in the Tyrol, he identified the remains of sixty different kinds of insects--ants, ichneumons, beetles, bugs, flies, and so on. The Red German Campion (_Lychnis Viscaria_) has an extremely sticky ring below each joint of the stem and inflorescence, which is most fatal to any creature which attempts to climb to the flowers. Other instances, such as the Petunia or Moss Rose, will occur to the reader. Another familiar kind of barrier is the presence on the calyx or involucre of a palisade of stiff hairs or prickles, such as may be studied in the Thistles; in some plants a downward-pointing ring of stiff hairs at each joint serves the same purpose. In the Japanese Wineberry (_Rubus phœnicolasius_), often grown in gardens, the calyx, like the stem, is densely clothed with bright red slender spines (Fig. 17). It opens to allow the inconspicuous petals to expand, and then closes again and resumes its protective rôle till the scarlet fruit approaches maturity.

But it is in the flower itself that we find the most ingenious arrangements to encourage useful and discourage useless visitors, to assist the former to pollinate the flower, and while offering nectar to the welcome guest to deny it to the unwelcome. The first stage in this specialization is that the flower, instead of having its axis vertical, and facing the sky, is turned on its side by the curving of its stalk, and looks out horizontally. The effect of this is to cause a flying insect on approaching the flower to alight in a particular position--namely, on the lowest petal. Following on the adoption of this attitude the next stage in development is seen in the parts of the flower beginning to alter their shape and position relative to each other and often also their colour. Thus, beginning with a quite regular flower, we can arrange a series showing more and more asymmetry. The tendency is generally for the lowest petal to become enlarged and often conspicuously marked, providing a broad, convenient platform on which insects may alight, while the remainder form walls and roof, protecting the important parts within and by their shape, which is often narrowed and tubular behind, barring access to all but chosen visitors. To find a full series illustrating these transformations we do not need to go to plants widely separated in their affinities. In the Buttercup order (_Ranunculaceæ_) alone every gradation may be found. The flowers of the Buttercups themselves are upright and quite regular. In the Larkspur (_Delphinium_) the flower is turned on its side, and a puzzling combination of coloured sepals and petals--five bright blue unequal sepals and a single large purplish petal of peculiar shape with a long hollow spur behind--produces a quite irregular blossom. The process is carried farther again in the Monkshood (_Aconitum_), in whose well-known blue flower the sepals and petals combine to produce a strikingly irregular blossom, with the upper sepal arching over into a great hood protecting the rest of the flower. In such irregular flowers the essential parts--the pollen-producing and pollen-receiving portions, or stamens and stigma--also alter their position and form, and are so placed that an insect, visiting the flower to obtain nectar (which is generally stored at the back, well out of the way), must of necessity receive pollen on its body, and probably deposit pollen on the stigma. To describe the variety and ingenuity of these devices as found in different flowers might well occupy several chapters, and only one or two examples can be quoted here; familiar wild flowers are chosen, and the reader should examine them for himself to understand their structure. In the well-known Pea type, one great petal arches over the flower; two narrow ones stand one on either side; the remaining two stand on edge below, with their margins in contact, enclosing the stamens and pistil. An insect visiting the flower alights naturally on the _keel_ or pair of lower petals. Pressed down by its weight, these open, often with a sudden movement like bursting, and dust the insect with pollen. Compare also the flowers of the Snapdragons (_Antirrhinum_) and Toadflaxes (_Linaria_), in which the upper and lower lips of the corolla meet like a closed mouth, which can be forced open only by a strong insect like a bee, and is safe from predatory visits of smaller fry (Fig. 18). In the Sages (_Salvia_) the corolla is tubular at the base; there is a large lobed lip on which visiting insects alight, and a hooded roof above arching over the stamens and pistil, which are placed close against it, overhanging the entrance to the corolla-tube, at the base of which the nectar is stored. The stamens, only two of which are developed, have each a hinge near the top, the part above the hinge being like a curved rod supported near its middle. These two curved rods stand normally in a vertical position, so that their lower ends partly block the entrance to the tube; the pollen is borne at their upper ends. Should a bee insert its head down the tube in search of nectar, it pushes the lower ends of the hinged rods upwards, with the result that their upper ends swing downward against the bee’s back, dusting it with pollen just at that part of its body which, if the bee should visit a rather older flower, would come in contact with the stigma, the slender stalk of which (the _style_) increases in length during the period of flowering, and is in consequence the more liable to be encountered.

Only one more instance can be referred to, which can be tested by the reader any summer day wherever any of our native Orchids grow. In these, the most highly specialized of all plant groups as regards pollination by insects, the general arrangement of the flower is often somewhat similar in a general sense to the last case; but here the sepals and petals which between them form the platform, tube, sides, and roof of the flower, are all separate and often differently and elaborately coloured. The essential organs are greatly modified and hardly recognizable at first. There is only one stamen, producing two clusters of pollen, which are embedded in the roof of the flower. Each possesses a slender stalk which terminates in a little sticky disc which projects from the general surface. The pollen grains are held together in a mass by fine threads, and the whole with its stalk--the _pollinium_--resembles a lemonade bottle in shape. The stigma is also embedded, forming a sticky surface in the roof of the flower behind the stamen. When an insect inserts its head into the flower, its forehead comes in contact with the sticky ends of the pollinia, which adhere, so that on leaving the flower the insect flies away with the pollen sticking to its forehead like two little horns. And now a remarkable thing happens. The stalks of the pollinia, drying rapidly in the air, contract unequally, and become curved, so that the pollinia bend forward into a horizontal position. When the insect visits another flower and thrusts in its head, the pollen consequently comes in contact with the sticky stigmatic surface farther down the tube, and cross-pollination is effected.

In the cases of many of these highly specialized flowers, one is no less struck with the perfection of the arrangements made for preventing self-pollination, than those adapted to securing cross-pollination. But in a few, on the contrary, self-pollination is specially arranged for.

It must be pointed out that the insects which pollinate these specialized flowers have in many cases acquired modifications in their structure corresponding to the modifications in the flowers which they frequent. In the more specialized forms, indeed, plant and animal have become entirely dependent on each other; the plants would become extinct in the absence of the special insects through whose agency they are able by pollination to produce fertile seed; and the insects would likewise die out if the flowers to whose nectar and pollen they look for food were not available.

As regards the kinds of insects which visit flowers for food, these are very numerous and belong to almost every section of that large class. In many, such as Neuroptera, Orthoptera, Hemiptera, Coleoptera, there is very little special adaptation for their flower-feeding habits, and these insects visit flowers, such as the _Umbelliferæ_, in which the nectar and pollen are freely exposed, and lie open to all. Many of the Diptera, or Flies, are in the same case; but in some families, such as the _Bombyliidæ_, high specialization for securing food from flowers is found: the creatures are provided with elongated probosces for sucking nectar even when it is deeply hidden, and no other food is used by the insects in their adult stage. But it is among the long-tongued Bees and the Lepidoptera (Butterflies and Moths) that the highest degree of adaptation in this direction is found; and the modifications are associated with those flowers which have become most highly specialized for insect pollination, and most completely dependent on it. In the Bees the legs have become much modified for the gathering of pollen, and the mouth is a long flexible sucking-tube which when not in use is carried rolled up in a spiral. The pollen, on which food alone the young bees are fed, is gathered and stored among rows of hairs on the legs, and in the more highly specialized forms it is wetted with honey so as to form a compact mass, easily carried and easily removed when the nest is reached. The balls of pollen thus formed are sometimes nearly the size of the body of the bee, and may contain one to two hundred thousand grains of pollen. The formation of the mouth is beautiful and complicated, adapted to the rapid sucking up of nectar even if deeply placed in the flower. The nectar is stored in the body of the bee, and subsequently transferred to the waxen honey-cells in the hive. In the Butterflies and Moths the mouth parts are also modified for sucking, and as these insects do not build nests or take care of their offspring as Bees do the mouth is formed solely for the purpose of securing the nectar which is their only food. The proboscis varies greatly in length in different groups, according to the kind of flower which they visit. In the Owl Moths (_Noctuidæ_) it is sometimes only eight millimetres (1/3 inch) long; in many of the Butterflies it is about half an inch. In the Hawk-moths it attains a remarkable development, necessitated no doubt by the habit of these insects of not alighting on or entering a flower, but hovering in front of it as a Humming Bird does, and sucking up the nectar while thus poised. The proboscis of the Convolvulus Hawk-moth measures 65 to 80 millimetres (2-1/2 to 3-1/4 inches), and some of the Tropical allies of this moth have probosces twice or even three times that length. These species feed on the nectar of flowers with tubular corolla of corresponding dimensions. Most of the Hawk-moths feed only at dusk, and as the time is short they take advantage of their powers of rapid flight to visit (and incidentally to pollinate) a very large number of flowers in a short period. Moreover, in common with most of the more specialized flower-feeding insects, they do not visit the flowers of different species indiscriminately, but dash to blossom after blossom of whatever single species they have selected. Hermann Müller records watching Humming-bird Hawk-moths (_Macroglossa stellatarum_) at work at the summit of the Albula Pass; one visited 106 flowers of _Viola calcarata_ in under 4 minutes; another 194 blossoms of the same plant in 6-3/4 minutes.

The day-flying Butterflies display none of this restless energy. The sunshine is pleasant and the day long. They wander aimlessly in their beauty from flower to flower, sun themselves on the warm ground, or “whirl through the air with the first good comrade that by chance appears.” They are the flowers of the air, and our country rambles are made more joyous by their careless companionship.