252 



SCIENCE OF AGRICULTURE. 



II. 



the 50 stamens of Barringtonja, theSSO of Thea, and the 80 of the Caryophyllus fecundate only two or three 

 ovules. 



Sect. IX. The Projyagation of the Species. 

 1639. As the life of the vegetable, like that of the animal, is limited to a defnite period, 

 and as a continued supply of vegetables is always wanted for the support of animals, 

 what we call art, or nature operating by means of the animal man, has taken care to 

 institute such means as shall secure the multiplying and perpetuating of the species in 

 all possible cases. 



1640. Equivocal seneratJon. It was long a vulgar error, countenanced even by the philosophy of the 

 times, that vegetables do often spring up from the accidental mixture of earth and putrid water, or other 

 putrid substances, in the manner of what was called the equivocal generation of animals ; or, at the very 

 least, that the earth contains the principle of vegetable life in itself, which, in order to develope, it is only 

 necessary to expose to the action of the air. The former alternative of the error has been long ago re- 

 futed ; the latter has lost its hold, having been refuted by Malpighi, who proved that the earth produces 

 no plant without the intervention of a seed, or of some other species of vegetable germ deposited in it by 

 nature or by art. 



1641. Fropagntion by seeds. When the seed has reached maturity in the due and 

 regular course of the developement of its several parts, it detaches itself sooner or later 

 from the parent plant, either singly or along with its pericarp, and drops into the soil, 

 where it again germinates and takes root, and springs up into a new individual. Such 

 is the grand means instituted by nature for the replenishing and perpetuating of the 

 vegetable kingdom. 



1642. Dispersion of seed. If seeds were to fall into the soil merely by dropping down from the plant, 



then the great mass of them, instead of germinating and springing up into distinct plants, would grow up 



only to putrefy and decay; to prevent which consequence 



nature has adopted a variety of the most efficacious contri. 



vances, all tending to the dispersion of the seed. The first 



means to be mentioned is that of the elasticity of the peri- 

 carp of many fruits, by which it opens when ripe, with a sort 



of sudden spring, ejecting the seed with violence, and throw- 

 ing it some considerable distance from the plant. This may be 



exemplified in a variety of cases ; the seeds of oats when ripe 



are projected from the calyx with such violence, that in a fine 



and dry day you may even hear them thrown out with a 



slight and sudden snap, in passing through a field that is ripe. 



The pericarp of the dorsiferous ferns {fig. 197.) is furnished 



with a sort of peculiar elastic ring, intended, as it would 



appear, for the very purpose of projecting the seeds. The 



capsules of the squirting cucumber, geranium, and Fraxinella, 



discharge their seeds also when ripe with an elastic jerk. But 



the pericarp of Impatiens, which consists of five cells with 



five valves, exhibits perhaps one of the best examples of this 



mode of dispersion. If it be accidentally touched when ripe 



it will immediately burst open, while the valves, coiling 



themselves up in a spiral form, and springing from the stem, 



discharge the contained seeds, and scatter them all around. 



The bursting of the pericarp of some species of pines is also 



worthy of notice. The pericarp, which is a cone, remains 



on the tree till the summer succeeding that on which it Was 



produced, the scales being still closed: but when the hot 



weather has commenced and continued for some time, so as 



to dry the cone tiioroughly, the scales open of their own 



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 



^vena fAtua {fig. 198.) or wild oat, as well as that of Erbdium cicutarium, and some others, seems to have 



been intended particularly for the purpose of aiding the further dispersion of the seed, after 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 

 often 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 

 andshirt 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. 

 16i3. Where distance of (iispersto7ii&TGq}\iTed,r\?iX\ire\s 



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 



