It is easy enough to comprehend the "wherefore" of the monkey pots, and their movable lids, but it is not so evident why, in similar trees of the same family, the seeds should be enclosed in hard, woody capsules, with no orifice, and from which there is no escape, but by the decay of the thick envelope. Such are the Brazil nuts of commerce (Bertholletia excelsa). "The fruit, round like a cannon ball, and about the size of a twenty-four pounder, is harder than the hardest wood, and has to be battered to pieces with the back of a hatchet to disclose the nuts. Any one who has hammered at a Bertholletia fruit will be ready to believe the story that the Indians, fond as they are of the nuts, avoid the 'totocke' trees till the fruit has all fallen for fear of fractured skulls." The Capuchin monkeys, according to Humboldt, "are singularly fond of these 'chestnuts of Brazil,' and the noise made by the seeds when the fruit is shaken as it falls from the tree excites their appetency to the highest degree." He does not, however, believe the story current on the Orinoco, that the monkeys place themselves in a circle, and by striking the shell with a stone succeed in opening it. That they may try is possible enough, for there is no doubt that monkeys do use stones to crack nuts. The impossibility in this case would be, not in the want of wits, but want of strength; and the monkeys must have too often to wait till the rainy season, when the shell rots of itself, and amuse themselves meanwhile in rolling the fruit about, vainly longing to get their paws in through the one little hole at its base.
Another instance of these wholly closed capsules is the fruit of the cannon-ball tree (Couroupita guianensis). This fruit "is a rough brown globe, as big as a thirty-two pound shot, which you must get down with a certain caution, lest that befal you which befel a certain gallant officer on the mainland of America. For, fired with a post-prandial ambition to obtain a cannon ball, he took to himself a long bamboo, and poked at the tree. He succeeded, but not altogether as he had hoped. For the cannon ball, in coming down, avenged itself by dropping exactly on the bridge of his nose, felling him to the ground, and giving him such a pair of black eyes that he was not seen on parade for a fortnight."
It has been suggested that, in such trees as the Brazil nut, which is produced in forests swarming with monkeys, that the closed capsule is a protection, and that if the capsule had been an open one, not only would Brazil nuts make less appearance in the markets of the world, but the trees would run a risk of extirpation. We must confess that we are not prepared to accept this as a sufficient reason for the closed capsule. Monkey pots are open capsules, and the trees are not yet extirpated; yet monkeys are as delighted with the "sapucaia" as with the "Brazil nut." In such a case speculation does little good, when it is simply an excuse for one's own ignorance.
<!-- image -->Fig. 65.—Fruit of the Cannon-ball tree (Couroupita guianensis).
In many cases there appears to be no special provision for the dispersion of seeds, and yet, when duly considered, such a future has not been disregarded. It may be that, covered with a pulpy fruit, attractive to some member of the animal kingdom, the hard seeds have thus been transported to a considerable distance, and found a congenial soil. This fact is recognised by zoologists themselves, as will be evident from the following extract:—"Doubtless many of our most richly-wooded landscapes owe much of their timber to the agency of quadrupeds and birds. Linnets, goldfinches, thrushes, goldcrests, &c., feed on the seeds of elms, firs, and ash, and carry them away to hedge-rows, where, fostered and protected by bush and bramble, they spring up, and become luxuriant trees. Many noble oaks have been planted by the squirrel, who unconsciously yields no inconsiderable boon to the domain he infests. Towards autumn this provident little animal mounts the branches of oak trees, strips off the acorns and buries them in the earth, as a supply of food against the severities of winter. He is most probably not gifted with a memory of sufficient retention to enable him to find every one he secretes, which are thus left in the ground, and springing up the following year, finally grow into magnificent trees. Pheasants devour numbers of acorns in the autumn, some of which having passed through the stomach, probably germinate. The nuthatch in an indirect manner also frequently becomes a planter. Having twisted off their boughs a cluster of beech-nuts, this curious bird resorts to some favourite tree, whose bole is uneven, and endeavours by a series of manoeuvres to peg it into one of the crevices of the bark. During the operation it oftentimes falls to the ground, and is caused to germinate by the moisture of winter. Many small beeches are found growing near the haunts of the nuthatch, which have evidently been planted in the manner described."
Not only do the birds and small quadrupeds assist in the dispersion of seeds in the way just indicated but even to a much greater extent. As, for instance, we have seen amongst the droppings of birds the small undigested seeds of pulpy fruits which they devoured, which seeds retained all their powers of germination, especially of elderberries and mulberries. This mode of dispersion is undoubtedly a very extensive one in practice. Neither can we ignore altogether the service which some insects may render in the dispersion of minute organisms. To what extent this may be carried it is difficult to determine, but we may give an illustration. It is not an unusual circumstance to find, when examining a species of black mould or of Torula, growing on rotten wood, that insects have been at work, destroyed the threads, and left behind them characteristic cylindrical exuviae. These undoubtedly had passed through their bodies, for fragments of threads were mixed with the spores. On two or three occasions we have determined that such spores still possessed the power of germination, even perhaps in an increased degree. These insects may assist in the dissemination of such spores, as molluscs do in feasting on the gills of an agaric, and then retiring to the shelter of some prostrate trunk. These speculations, however, concern a very minute class of organisms which, as a rule, we have deemed it prudent to ignore in this volume.
Then there are larger animals which contribute their share to the dissemination of plants, and especially those of the human family. It would be impossible to enter fully on such a topic, at the end of a chapter, but one or two brief suggestions may be permitted. Even to the present day, writes Schleiden, are marked the footsteps of the bands of nations which in the middle ages emerged from Asia into Central Europe, by the advance of the Asiatic steppe plants, such as the kochia and the Tartar sea-kale, the former into Bohemia and Carniola, the latter into Hungary and Moravia. The North American savage significantly calls our plantain (Plantago major), or road weed, the "footstep of the whites," and a common species of vetch (Vicia cracca) still marks the former abode of the Norwegian colonists in Greenland. One of the most striking instances of this kind is the gradual extension of the thorn apple over the whole of Europe, which has followed the bands of gipsies out of Asia; this race make frequent use of this poisonous plant in their unlawful proceedings, and hence much cultivated by them, it also occurs, uncalled for, near the place where they have made their habitations. Auguste St. Hilaire says, "In Brazil, as in Europe, certain plants appear to follow in the footsteps of man, and preserve the traces of his presence; frequently have they helped me to discover the situation of a ruined hut, in the midst of the wastes which extend out beyond Paracuta. Nowhere have the European plants multiplied in such abundance as in the plains between Theresia and Monte Video, and from this city to the Rio Negro. Already have the violet, the borage, some geraniums, the fennel, and others, settled in the vicinity of Sta. Theresia. Everywhere we found our mallows and camomiles, our milk-thistle, but, above all, our artichokes, which, introduced into the plains of the Rio de la Plata, and the Uruguay, now clothe immeasurable tracts, and render them useless for pasture." After the War of Deliverance, in many places where the Cossacks had encamped, was found the tick-seed, a plant allied to the goosefoots, which is quite exclusively indigenous in the steppes on the Dnieper, and in a similar manner was Bunias orientale spread with the Russian hosts, in 1814, through Germany even to Paris.
A curious circumstance has been recorded as this chapter is passing through the press, which deserves permanent record, albeit, it would have been more in place in the seventh chapter. An Indian species of Loranthus, which is a parasite like the mistletoe, grows on evergreen trees, especially Memecylon. The fruit is a viscid pulp, which surrounds the seed and adheres to whatever it falls upon, until the seed germinates. The peculiar locomotion now recorded is confined to the first stage of germination of the seed, and indicates a rambling habit for the purpose of securing a suitable home. The radicle at first grows out, and when it has grown to about an inch in length, it developes upon its extremity a flattened disc; the radicle then curves about until the disc is applied to any object that is near at hand. If the spot upon which the disc has fastened is suitable, the germination continues, and no locomotion takes place; but if the spot should not be a favourable one, the germinating embryo has the power of changing its position. This is accomplished by the adhesive radicle raising the seed and advancing it to another spot, or, to make the process plainer, the disc at the end of the radicle adheres very tightly to whatever it is applied to; the radicle itself straightens, and tears away the viscid berry from whatever it has adhered to, and raises it in the air. The radicle then again curves, and the berry is carried by it to another spot, where it adheres again. The disc then releases itself, and by the curving about of the radicle is advanced to another spot, where it again fixes itself. This, Dr. Watt says, he has seen repeated several times, so that to a certain extent the young embryo, still within the seed, moves about. It seems to select certain places in preference to others, particularly leaves. The berries on falling are almost certain to alight upon leaves, and although many germinate there, they have been observed to move from the leaves to the stem, and finally fasten there.
CHAPTER XV
MIMICRY.
IN the animal kingdom certain resemblances between the members of one group and those of another, considerably removed from it in the system of classification, have of late years been the subject of much discussion. On the supposition that these resemblances have been acquired, and are designed to serve some purpose in the economy of nature, the term "mimicry" has been applied to them. Subsequently it has been proposed to substitute another term, that of "homoplasy," but this has not met with general acceptance; we have, therefore, adopted the older term. Mr. H. W. Bates first introduced the subject to notice, with some very striking examples of "mimetic resemblances" in Lepidopterous insects, which have since been much augmented by others. Very few allusions have hitherto been made to such resemblances in plants, although Mr. A. Bennett has opened the question, and with these organisms the subject is still in a very elementary stage. It shall be our purpose to indicate such examples as have come to our knowledge, but rather as a record of facts than with any design to theorise about them. In animals it has been contended that the resemblances are acquired by natural selection and the survival of the fittest, such resemblances being for the benefit of the organisms which acquire them. The data are at present insufficient to apply such a theory to plants, but the instances are sometimes so striking and curious that they could not be ignored as remarkable phenomena in plant life.