252 SCIENCE OF AGRICULTURE. Part II. 



accord with a sudden jerk, ejecting the contained seeds : and if a number of them happen to burst together, 

 which is often the case, the noise is such as to be heard at some considerable distance. The twisted awn of 

 avena fatua {fig. 240.), or wild oat, as well as that of geranium cicutarium, and some others, seems to liave 

 been intended particularly for the purpose of aiding the further dispersion of the seed, alter being discharged 

 from the plant or pericarp. This spiral awn or spring, 

 which'is beset with a multitude of fine and minute hairs, 

 possesses the property of contracting by means of drought, 

 and of expanding by means of moisture. Hence it remains 

 of necessity in a perpetual state of contraction or dilatation, 

 dependent upon change of weather ; from which, as well as 

 from the additional aid of the fine hairs, which act as so many 

 fulcra, and cling to whatever object they meet, the seed to 

 which it is attached is kept in continual motion till it either 

 germinates or is destroyed. The awn of barley, which is 

 beset with a multitude of little teeth all pointing to its 

 upper extremity, presents also similar phenomena. For 

 when the seed with its awn falls from the ear and lies flat 

 upon the ground, it is necessarily extended in its dimensions 

 by the moisture of the night, and contracted by the drought 

 of the day. But as the teeth prevent it from receding in 

 the direction of the point, it is consequently made to ad- 

 vance in the direction of the base of the seed, which is thus 

 otlen carried to the distance of many feet from the stalk on 

 which it grew. If any one is yet sceptical with regard to 

 the travelling capacity of the awn, let him only introduce 

 an awn of barley with the seed uppermost between his coat 

 and shirt sleeve at the wrist, when he walks out in the morn- 

 ing, and by the time he returns to breakfast, if he has 

 walked to any great distance, he will find it up at his arm- 

 pit. This journey has been effected by means of the con- 

 tinued motion of the arm, and consequently of the teeth of 

 the awn acting as feet to carry it forward. 



1610. Where distance of dispersion '\s reqxnreA, n&tnre 15 



also furnished with a resource. One of the most common modes by which seeds are conveyed to a dis- 

 tance from their place of growth is that of the instrumentality of animals. Many seeds are thus carried to 

 a distance from their place of growth merely by their attaching themselves to the bodies of such animals 

 as may happen accidentally to come in contact with the plant in their search after food ; the hooks or hairs 

 with which one part or other of the fructification is often furnished serving as the medium of attachment, 

 and the seed being thus carried about with the animal till it is again detached by some accidental cause, and 

 at last committed to the soil. This maybe exemplified in the case of the bidens and myosotis, in which 

 the hooks or prickles are attached to the seed itself ; or in the case of galium aparine and others, in which 

 they are attached to the pericarp ; or in the case of the thistle and the burdock, in which they are attached 

 to the general calyx. Many seeds are dispersed by animals in consequence of their pericarps being used 

 as food. This is often the case with the seeds of the drupe, as cherries, sloes, and haws, which birds 

 often carry away till they meet with some convenient place for devouring the pulpy pericarp, and 

 then drop the stone into the soil. And so also fruit is dispersed that has been hoarded for the winter, 

 though even with the view of feeding on the seed itself, as in the case of nuts hoarded up by squirrels, 

 which are often dispossessed by some other animal, that not caring for the hoard scatters and disperses it. 

 Sometimes the hoard is deposited in the ground itself, in which case part of it is generally found to take 

 root and to spring up into plants. Tliough it has been observed that the ground-squirrel often deprives the 

 kernel of its germ before it deposits the fruit it collects. Crows have been also observed to lay up acorns 

 and other seeds in the holes of fence-posts, which being either forgot or accidentally thrust out, fall ulti- 

 mately into the earth and germinate. But sometimes the seed is even taken into the stomach of the 

 animal, and afterwards deposited in the soil, having passed through it unhurt. This is often the case with 

 the seed of many species of berry, such as the mistletoe, which the thrush swallows and afterwards deposits 

 upon the boughs of such trees as it may happen to alight upon. The seeds of the loranthus americanus, 

 another parasitical plant, are said to be deposited in like manner on the branches of the cocoloba grandi- 

 flora, and other lofty trees ; as also the seeds of jfhytolacca decandra, the berries of which are eaten by 

 the robin, thrush, and wild pigeon. And so also the seeds of currants or roans are sometimes deposited, 

 after having been swallowed by blackbirds or other birds, as may be seen by observing a currant-bush or 

 young roan-tree growing out of the cleft of another tree, where the seed has been left, and where there 

 may happen to have been a little dust collected by way of soil ; or where a natural graft may have been 

 effected by the insinuation of the radicle into some chink or cleft. It seems indeed surprising that any 

 seeds should be able to resist the heat and digestive action of the stomach of animals ; but it is undoubtedly 

 the fact. Some seeds seem even to require it. The seeds of magnolia glauca, which have been brought 

 to this country, are said to have generally refused to vegetate till after undergoing this process, and it is 

 known that some seeds will bear a still greater degree of heat without any injury. Spallanzani mentions 

 some seeds that germinated after having been boiled in water : and Du Hamcl gives an account of some 

 others that germinated even after having been exposed to a degree of heat measuring 9S5 of Fahrenheit. 

 In addition to the instrumentality of brute animals in the dispersion of the seed might be added also that 

 of man, who, for purposes of utility or of ornament, not only transfers to his native soil seeds indigenous 

 to the most distant regions, but sows and cultivates them with care. 



1611. The agencij of winds is one of the most effective modes of dispersion instituted by nature. Some 

 seeds are fitted for this mode of dispersion from their extreme minuteness, such as those of the mosses, 

 lichens, and fungi, which float invisibly on the air, and vegetate wherever they hapi)en to meet with a 

 suitable soil. Others are fitted for it by means of an attached wing, as in the case of the fir-tree and 

 liriodendron tulipifera, so that the seed, in falling from the cone or capsule, is immediately caught by the 

 wind, and carried to a distance. Others are peculiarly fitted for it by means ol their being furnished with 

 an aigrette or down, as in the case of the dandelion, goat's-beard, and thistle, as well as most plants of the 

 class Si/ngenesia ; the down of which is so large and light in proportion to the seed it supports, that it is 

 wafted on the most gentle breeze, and often seen floating through the atmosphere in great abundance at 

 the time the seed is ripe. Some have a tail, as in clematis vita alba. Others are fitted for this mode of 

 dispersion by means of^the structure of the pericarp, which is also wafted along with them, as in the case of 

 staphylea trifolia, the inflated capsule of which seems as if obviously intended thus to aid the dispersion 

 of the contained seed by its exposing to the wind a large and distended surface with but little weight. And 

 so also in the case of the maple, elm, and ash, the capsules of which are furnished, like some seeds, with 

 a membranous wing, which when they separate from the plant the wind immediately lays hold of and 

 drives before it. 



1612. The instrunientality of strea^ns, rivers, and currents of the ocean, is a further means adopted by 

 nature for the dispersion of the seeds of vegetables. The mountain.stream or torrent washes down to 

 the valley the seeds which may accidentally fall into it, or which it may happen to sweep from its banks 

 when it suddenly overflows them. The broad and majestic river, winding along the extensive plain, and 

 traversing the continents of the world, conveys to the distance of many hundreds of miles the seeds that 

 may have vegetated at its source. Thus the southern shores of the Baltic are visited by seeds which grew 



