brushes and thickets of hairs are present, guarding the entrance and rendering access difficult, whilst still allowing it. Large and powerful animals find these obstacles no hindrance, and readily brush them aside; small ones, however, cannot do this, but have to climb over or circumvent the obstacles. And in many cases this enforced divergence by small insects from the direct path brings about the desired result. For, in circumventing these folds and barricades and hairs, they are unconsciously led past the anthers and stigmas, contact with which is unavoidable. Thus, what would otherwise be useless visitants become welcome

guests. They are conducted indirectly to the honey by these curious structures, which may, in a sense, be termed 'path-finders'." Cursory examination of such flowers as Foxglove or Pansy will show the presence of barricades of the kind mentioned (see also fig. 1085). Path-finders for the guidance of invited guests are often present in the form of conspicuous colour-streaks, which converge towards the source of nectar. Pansy, Azalea, and PelarHoneysuckle (Lonicera alpigena), showing gonium are particularly good examples of this.

Fig. 1085.-Section through Flower of a

protective tufts of hair; enlarged

The defences and other arrangements which have been evolved in various connections by plants and animals are never completely successful, and with changed surroundings are apt to fail. This applies not only to "mice and men ", but also to flowers. Kerner states, for example, that the flowers of some 300 European plants are systematically robbed by humble-bees, which take a short cut to the nectar by biting through the calyx or corolla. The result may be disastrous, for in some of these plants but few seeds are produced, so that they are becoming rare, and in course of time will probably die out altogether. Certain Alpine Catch-Flies (Silene Pumilio and S. Elizabetha) are in this evil case. Kerner suggests

that such plants date back to a time when there were no, or but few, humble-bees in the region where they now grow, and that they have since failed to evolve means of defence against the new kind of attack.

Wingless enemies of soft-bodied character, especially snails

and slugs, are not kept off by smooth surfaces or sticky secretions. But such creatures are easily baffled by prickles, bristles, thorns, and other sharp structures, and these are often found in the neighbourhood of the flowers.

DISPERSAL OF PLANTS BY ANIMALS.-Since the large majority of plants are fixed, means of dispersal are clearly a necessity, as otherwise they would have to struggle for existence with their own offspring. And it is only when numerous individuals of a species are placed in favourable surroundings that the species has any chance of escaping extinction. It is not therefore surprising to find that there are almost innumerable ways by which dispersal is effected. Sometimes the plant itself is the agent, sending out creeping stems above or below ground, or ejecting its fruits, seeds, or spores to a distance by explosive or elastic mechanisms. Currents of air and water are also of great importance in this connection. But we are here only concerned with the chief ways in which animals are pressed into the service of plants for this purpose, or it may be render assistance of more casual kind.

Many of the small plants which float in ponds, such as Duckweeds (Lemna) and various algæ, must often cling to the legs of water-birds, and get carried bodily from place to place. And it is noticeable that the buds of somewhat larger aquatic plants, such as Frog-bit and Bladderwort (Hydrocharis and Utricularia), possess a slimy covering by means of which they readily adhere to the plumage of such birds. Among marine plants a curious means of transit is exemplified by various sea-weeds which certain crabs plant on their backs to make themselves inconspicuous (see vol. ii, p. 287). On the decease of such a crab his little “garden" goes on growing, unless perchance he has been swallowed whole by some predaceous form.

A good many land-plants propagate by means of "offshoots", i.e. specialized branches, &c., which grow into new individuals, and cases have been noted where animals assist in the dispersal of such offshoots. Some of the rounded Mexican Cacti (species of Mammillaria), for example, produce little spherical shoots studded with barbed bristles, and which are very readily detached from the parent plant. They readily cling to the coats of various mammals and may thus be carried for a considerable distance.

Dispersal of Seeds and Fruits by Animals.-As already explained (p. 85), a seed may be regarded as a matured ovule,

in which is contained a dormant plantlet, that has resulted from the fertilization of an egg-cell. The fertilizing process stimulates the growth of various parts external to the ovules, leading to the production of what may broadly be called a "fruit", which for our present purpose may be considered as a seed-carrier. A cherry or plum, for example, is a fruit, within which is a single seed-the "stone". A long account of the different kinds of fruit would be out of place here, but it may be well to add that many are hard and dry, e.g. hazel-nuts (of which the "kernels" are the seeds), poppy-" heads ", and the so-called “seeds" of Sunflower or Carrot.

The dispersal of seeds in many plants results from the fact that a considerable number of animals are fruit-eaters. And in such cases the seeds being protected by hard coats often escape digestion. It would appear that the attractive colours and palatable qualities of numerous fruits have been evolved with direct reference to this. While still unripe such fruits are inconspicuous and more or less nauseous, but become extremely conspicuous by the time they are ready for consumption, thus advertising their desirable properties as articles of diet. Though monkeys and other fruit-eating mammals no doubt largely assist in plant dispersal, birds seem to play a more important part in the matter. Kerner made a large number of experiments which tend to prove this. He found, for example, that the hard-coated seeds of stone-fruits and berries passed quite uninjured through the bodies of ravens and jackdaws; also that the blackbird, songthrush, rock-thrush, and robin, which eagerly devour fleshy fruits, throw up the seeds if these are large, as in Barberry and Privet. The fate of small seeds swallowed by the last four birds is thus described by him (in The Natural History of Plants):-" Of the fruits and seeds which passed through the intestine of one or other of these birds, 75 per cent germinated in the case of the blackbird, 85 per cent in the case of the thrush, 88 per cent in the case of the rock-thrush, and 80 per cent in the case of the robin. . . . From these experiments it is evident that the dispersal of edible fruits through the agency of thrushes and blackbirds is not, as was formerly supposed, an exceptional phenomenon obtaining in the mistletoe only, but one that may take place in the case of many other plants, and other observations prove that, as a matter of fact, it does take place."

Some animals store up seeds and fruit for future use, and as for various reasons many of these escape being eaten, the storing habit undoubtedly promotes dispersal. Squirrels, jays, and many ants may be cited in illustration. The case of ants is peculiarly interesting. According to Kerner's observations the seeds which prove attractive to these little creatures are those which, although smooth, possess a little rough outgrowth technically known as a "caruncle", as in Violet, Greater Celandine, Snowdrop, Periwinkle, and some Spurges. It is only this caruncle which is eaten, the rest of the seed being left untouched, and capable of germination.

Besides the seeds and fruits which specially appeal to the appetites of animals, there are many others which become attached to their bodies, and are thus effectively dispersed. This may take place without any special adaptations to clinging, as in the case of the floating seeds of many aquatic plants, which adhere to the plumage of birds, or where moist earth

containing seeds sticks to the feet of birds or other animals.

Fig. 1086.-Fruit of Linnaa borealis (× 5) studded with glandular hairs

There are, however, a large number of fruits and seeds which are either sticky or else studded with hooks, their chances of transport by animals being thus greatly increased. Stickiness results in many cases from exposure to moisture, as in the seeds of Meadow Saffron (Colchicum) which have often been observed adhering to the feet of sheep, cattle, and horses. A somewhat more specialized case is afforded by fruits which owe their viscidity to the presence of glandular outgrowths, e.g. Linnæa borealis (fig. 1086).

A firmer means of attachment is found in seeds and fruits provided with hooks, and its efficiency would seem to be proved by the fact that about ten per cent of Flowering Plants are provided with such arrangements. They have apparently been evolved, at least in many cases, in relation to the hairy coats of Mammals, for they are particularly characteristic of plants of low stature, with which such animals are likely to come into contact. Many examples are found among the members of our native flora, as everyone who knows the country must have observed. The little globular fruits of the Goosegrass or Cleavers (Galium aparine, fig. 1087) are studded with little recurved bristles which prove very effective holdfasts, and the "burrs

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of Burdock (Arctium majus, fig. 1088) cling with great tenacity to sheep and other animals. Each burr consists of a number of fruits enclosed by a great many narrow scales, each one of

which is bent into a hook at its tip. A different but equally effective arrangement is present in Avens (Geum urbanum, fig. 1088). The group of fruits is not surrounded by clinging scales, but each is provided with a long hook. In some foreign fruits the holdfasts are of formidable character, and cause much pain to the unfortunate animals which unwillingly promote dispersal. A well-known instance is that of the Harpoon-Plant (Harpagophytum) of South Africa, the large fruits of which are covered with stout radiating projections provided with powerful hooks. They are the source of much inconvenience to such animals as antelopes and lions, being said to sometimes cause the death of the latter.

Dispersal of Spores by Animals.-Fleshy fungi are eaten by various insects that swallow vast numbers of the minute spores

by which such plants propagate, these passing uninjured through their bodies. In some cases flies are attracted by a sweet fluid (as in Ergot, Claviceps purpurea), or by evil-smelling moisture that exudes on the spore-producing surface (as in the Stinkhorn, Phallus impudicus). Earth-Worms and other burrowing forms no doubt help to disperse the spores of underground fungi, such as truffles. The lastnamed plants are also eagerly sought and devoured by pigs, with similar results. The dissemination by animals of disease-producing bacteria is too notorious to require emphasizing.

Fig. 1088.-Group of Hooked Fruits of Avens

(Geum urbanum) is shown to left, with a single fruit

on larger scale. On the right is shown a group of

the Fruits of Burdock (Arctium majus) surrounded

by hooked scales.