254 SCIENCE OF AGRICULTURE. Part II. 



also, according to Gfsrtner, propagated only by gems ; while Maichkntia, Anth6ceros, Jungermannia, and 

 Lycopt^rdon, are said to be propagated both by gems and seeds. 



1650. Runners are young shoots issuing from the collar or summit of the root, and creeping along the 

 surface of the soil ; but producing a new root and leaves at the extremity, and forming a new individual, 

 by the decay of the connecting link, as in the strawberry. 



Ifijl. Slips. The process of raising perennials by slips" is well known to gardeners, and should, perhaps, 

 be regarded as an extension of the old plant, rather than as the generation of a new one; though it serves 

 the purpose of the cultivator equally well as a plant raised from seed, with the additional advantage of 

 bearing fruit much sooner. But how is the root generated which the slip thus produces ? If the trunk of 

 a tree is lopped, and all its existing buds destroyed, then there will be protruded from between the wood 

 and bark a sort of protuberant lip or ring formed from the proper juice, and from which there will spring 

 a number of young shoots. The formation of the root, in the case of the slip, is eff'ected in the same man- 

 ner, the moisture of the soil encouraging the protrusion of buds at and near the section ; and the bud that 

 would have been converted into a branch above ground is converted into a root below. 



l(it>2. Layers. The mode of propagation by layers is practised upon trees that are delicate, and which 

 cannot readily be propagated by means of slips ; in which case the root is generated nearly as in the former 

 case, the soil stimulating the protrusion of buds which are converted into roots. In many plants, such as 

 the currant and laurel, this is altogether a natural process, effected by the spontaneous bending down of a 

 branch to the surface of the soil. 



1653. Suckers or offsets. Many plants protrude annually from the collar a number of young shoots, 

 encircling the principal stem and depriving it of a portion of its nourishment, as in the case of most 

 fruit trees. Others send out a horizontal root from which there at last issues a bud that ascends above the 

 soil, and is converted into a little stem, as in the case of the elm tree and Syringa. Others send out a hori. 

 zontal shoot from the collar or its neighbourhood ; or a shoot that ultimately bends down by its own weight 

 till it reaches the ground, in which it strikes root, and again sends up a stem as in the currant bush and 

 laurel. The two former are called suckers or offsets, though the term offset should, perhaps, be restricted 

 to the young bulbs that issue and detach themselves annually from bulbous roots. The latter is not desig- 

 nated by any particular name, but may be regarded as a sort of natural layer, resembling also, in some 

 respects, the runner ; from which, however, it is distinguished in that it never detaches itself spon. 

 taneously from the parent plant, as is the case also with the two former : but if either of them is arti- 

 ficially detached, together with a portion of root or a slice of the collar adhering to it, the detached part 

 will now bear transplanting, and will constitute a distinct plant. 



1654. Grafting and budding. The species is also often propagated, or at least the variety is multiplied, 

 by means oi grating ; which is an artificial application of a portion of the shoot or root of one tree or 

 plant to the stem, shoot, branch, or root of another, so that the two shall coalesce together and form but 

 one plant. The shoot which is to form the summit of the new individual is called the scion ; the stem to 

 which it is affixed is called the stock ; and the operation, when effected, the graft. As the graft is merely 

 an extension of the parent plant from which the scion came, and not properly speaking a new individual, 

 so it is found to be the best method of propagating approved varieties of fruit trees without any danger 

 of altering the quality of the fruit, which is always apt to be incurred in propagation from seed, but 

 never in propagating from the scion. The scion will also bear fruit much sooner than the tree that is 

 raised from seed ; and, if effected on a proper stock, will be much more hardy and vigorous than if left on 

 the parent plant. Hence the great utility of grafting in the practice of gardening. Till lately, grafting 

 was confined to the ligneous plants, but it is now successfully practised on the roots and shoots of her- 

 baceous vegetables ; and the dahlia is grafted by the root ; the melon on the gourd ; the love-apple on the 

 potato ; the cauliflower on the cal)bage, &c., by the shoot. A very ingenious tract has been published on this 

 subject, entitled, Essai sur la Greffe de I'Herbe des Plantes et des Arbres, par Monsr. le Baron de 

 Tschoudy, Bourgeois de Glaris. Paris, 1819. 



Sect. X. Causes limiting the Propagation of the Species. 



1655. Though plants are controlled chiefly by animals, yet they also control one another. 

 From the various sources of vegetable reproduction, but particularly from the fertility 

 and dispersion of the seed, the earth would soon be overrun with plants of the most pro- 

 lific species, and converted again into a desert, if it were not that nature has set bounds 

 to their propagation by subjecting them to the control of man, and to the depredations 

 of the great mass of animals ; as well as by confining the germination of their seeds to 

 certain and peculiar habitations arising from soil, climate, altitude, and other circum- 

 stances. In order to form an idea of the manner in which the latter act upon vegeta- 

 tion, imagine that every year an enormous quantity of seeds, produced by the existing 

 vegetables, are spread over the surface of the globe, by the winds and other causes already 

 mentioned ; all of these seeds which fall in places suitable for their vegetation, and are 

 not destroyed by animals, germinate and produce plants ; and then among these plants, 

 the strongest, and largest, and those to which the soil is best suited, develope themselves 

 in number and magnitude so as to choke the others. Such is the general progress of 

 nature, and among plants, as among animals, the strong flourish at the expense of the 

 weak. These causes have operated for such a length of time, that the greater number 

 of species are now fixed in, and considered as belonging to, certain soils, situations, and 

 climates, beyond which they seldom propagate, otherwise than by the hands of man. 



Sect. XI. Evidence and Character of Vegetable Vitality. 



1656. The power of counteracting the laws of chemical affinity is reckoned the best and 

 most satisfactory evidence of the presence and agency of a vital principle, as inherent in 

 any subject. This principle, which seems first to have been instituted by Humboldt, is 

 obviously applicable to the case of animals, as is proved by the process of the digestion 

 of the food, and its conversion into chyle and blood ; as well as from the various 

 secretions and excretions effected by the several organs, and causing the growth and 

 developement of the individual, in direct opposition to the acknowledged laws of 

 chemical affinity, which, as soon as the vital principle is extinct, begin immediately to 

 give evidence of their action, in the incipient symptoms of the putrefaction of the dead 

 body. But the rule is also applicable to the case of vegetables, as is proved by the 



