186 SCIENCE OF GARDENING. Fart II. 



and consequently not furnished with pollen. The confervas and ulvse, together with the genera Blasia 

 and Riccia, are also, according to Gsertner, propagated only by gems; while marchantia, anthoceros, 

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



838. 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. 



839. 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 

 effected in the same manner, 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. 



840. Layers. The mode of propagation by layers is practised uptm trees that are deli- 

 cate, 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. 



841. 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 nourish- 

 ment, 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 horizontal 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 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 designated by any particular name, but may be re- 

 garded 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 

 detached, together with a portion of root or a slice of the collar adhering to it, it will now 

 bear transplanting, and will constitute a distinct plant. 



842. Grafting and budding. The species is also often propagated, or at least the 

 variety is multiplied, by means of grafting, which is an artificial application of a portion 

 of the shoot or root of one tree gr 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 propagating 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 prac- 

 tised 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 cab- 

 bage, &c. by the shoot. A very ingenious tract has been published on this subject, 

 entitled, Essai sur la Greffe de Vherbe des plantcs et des arbres, par Mons. Le Baron de 

 Tschoudy, Bourgeois de Claris. Paris, 1819. 



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



843. Though jylants are controlled chiefly by animals, 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 control of man, and to the depredations of 

 the great mass of animals ; as well as in confining the germination of their seeds to cer- 

 tain and peculiar habitations arising from soil, climate, altitude, and other circumstances. 



