Book I. PROPAGATION OF THE SPECIES. 253 



in the interior of Germany, and the western shores of the Atlantic by seeds that have been generated in' 

 the interior of America. But fruits indigenous to America and the West Indies have sometimes been 

 found to be swept along by the currents of the ocean to the western shores of Europe. The fruit of 

 mimosa scandens, dolichos pruriens, guilandina bonduc, and anacardium occidentale, or cashew-nut, have 

 been thus known to be driven across the Atlantic to a distance of upwards of iilXM) miles ; and although 

 the Iruits now adduced as examples are not such as could vegetate on the coast on which they were thrown, 

 owing to soil or climate, yet it is to be believed that fruits may have been often thus transported to 

 climates or countries favorable to their vegetation. 



1613. Propagation by gems. I'hough plants are for the most part propagated by means of seeds, yet 

 many of them are propagated also by means of gems ; that is, bulbs and buds. 



1614. The cauUnary bulb is often the means of the propagation of the species : it generally appears in 

 the axil of the leaves, as in dentaria bulbifera and lilium bulb'iferum ; or between the spokes of their 

 umbels, as in allium canadense ; in the midst of the spike of flowers, as in polygonum viviparum and 

 poa alpina. As plants of this last kind are mostly alpine, it has been thought to be an institution or 

 resource of nature to secure the propagation of the species in situations where the seed may fail to ripen. 



1615. The bud, though it does not spontaneously detach itself from the plant and form a new individual, 

 will yet sometimes strike root and develope its parts if carefully separated by art and planted in the earth : 

 but this is to be understood of the leaf-bud only, for the flower-bud, according to Mirbel, if so treated, 

 always perishes. 



1616. Propagation by the leaves. The species may sometimes be propagated even by means of the 

 leaves ; as in the aloe, sea-onion, and some species of arum, which if carefully deposited in the soil will 

 grow up into new plants, by virtue, no doubt, of some latent gem contained in them. The fungi and 

 lichens, according to Ga;rtner, are all gemmiferous, having no sexual organs, and no pollen impregnat- 

 ing a germ. In the genus Lycoperdon, the gelatinous substance that pervades the cellular tissue is con- 

 verted into a proliferous powder ; in clavaria, the fluid contained in the cavities of the plant is converted 

 into a proliferous powder also ; and in the agarics, hypnum, and poletus, vesicles containing sobolifer- 

 ous granules are found within the lamina, pores, or tubes. Hedwig, on the contrary, ascribes to the 

 fungi a sexual apparatus, and maintains that the pollen is lodged in the volva. But here it is to be 

 recollected, as in the cases of the scutelte of the lichens, that all fungi are not furnished with a volva, 

 and consequently not furnished with pollen. The conferva and ulvae, together with the genera Blasia 

 and Riccia, are also, according to Ga^rtner, propagated only by gems ; while marchantia, anthoceros, 

 jungermannia, and lycoperdon, are said to be propagated both by gems and seeds. 



1617. i?Mrt^/-5 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. 



1618. 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 sUp 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 effected 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. 



1619. 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. 



1620. Suckers or off-sets. 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 thereat 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 neighborhood ; 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 off-sets, though the term off-set 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 spontaneously 

 from the parent plant, as is? the case also with the two former. But if either of them is artificially de- 

 tached, together with a portion of root or a slice of the collar adherring to it, it will now bear transplant- 

 ing, and will constitute a distinct plant. 



1621. Grafting and budding. The species is also often propagated, or at least the variety is multiplied, 

 byjmeans of grafting, 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 thegraft 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. And 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 herbaceous vegetables ; and the dahlia is grafted by the root ; the melon on the gourd ; the love-apple 

 on the potatoe ; the cauliflower on the cabbage, &c. by the shoot. A very ingenious tract has been pub- 

 lished on this subject, entitled, Essai sur la Cheffe de I'herbe des plantes et des arbres, par Monsr. Le 

 Baron de Tschoudy, Bourgeois de Claris. Paris, 1819. 



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



1622. Though plants are controlled clmjly by animalSf yet they also control one another. 

 From the various sources of vegetable reproduction, but particularly from the fer- 

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

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

 bounds to their propagation by subjecting them to the controul of man, and to the depre- 

 dations of the great mass of animals ; as well as in confining the germination of their 

 seeds to certain and peculiar habitations arising from soil, climate, altitude, and other 

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

 tion ; imagine that every year an enormous quantity of seeds, produced by the existiq^p 



