858 



SCIENCE OF AGRICULTURE. 



Pa.it II. 



-tamens of Barringtunfa, the ! 10 of Thai, and the BO of the Caryophyllus fecundate only two or three 

 ovule*. 



Sect. IX. The Propagation of the Species. 



infjf). As tlw Uf,- of the vegetable, Wee that of tin- animal, is limited to a definite period, 

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

 what we call ail, 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 generation. It «u long a vulgar error, countenanced even by the philosophy of the 

 tines, thai vegetable! do often spring up from the accidental mixture of earth and putrid water, or other 

 putt d lubstancet, in the manner of what was called the equivocal generation of animals ; or, at the very 

 I,, ,-t, thai the i srti contalna the principle ol vegetable life in itself, which, in order to develope, it is only 

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

 t,ii, ,i . the latter has lost it~ hold, having been refuted by Bfalpighi, who proved that the earth produces 

 no pi on n ithoul th. intervention oi ,1 seed, or of some other species of vegetable germ deposited in it by 

 Mature or bj art 



1641. Propagation 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 

 t'ro:i) 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. Disprrti m qf teed. 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 his 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 « Inn 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 

 ■ 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 oft he squirting cucumber, geranium, and Kraxinella, 

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

 the pericarp of Impatiens, which consists of five cells with 

 five valves, exh.oits 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. 

 'I'iie 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 thoroughly, 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 

 Av\ na fitua [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 themoistureof the night, and contracted by thedrought 

 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 

 tin- 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, anil 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. 



1643. Where distance qf dispersion is required, nature is 

 a!?o 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 



