Page:Encyclopædia Britannica, Ninth Edition, v. 12.djvu/247

235 PROPAGATION.] 235, Offsets. Tubers under the surface, the covering of the smaller ones especially being light and open. Many seeds grow well when raked in ; that is, the surface on which they are scattered is raked backwards and forwards until most of them are covered. Whatever the seeds, the ground should be made tolerably firm both beneath and above them; this may be done by treading in the case of most kitchen garden crops, which are also better sown in drills, this admitting the more readily of the ground being kept clear from weeds by hoeing. All seeds require a certain degree of heat to induce germination. For tropical plants the heat of a propagating house 75 to 80, with a bottom heat of 80 to 90 is desirable, and in many cases absolutely necessary ; for others, such as half-hardy annuals, a mild hot bed, or a temperate pit ranging from 60 3 to 70 3, is convenient ; while of course all outdoor crops have to submit to the natural temperature of the season. It is very important that seeds should be sown when the ground is in a good working condition, and not clammy with moisture. (2) By Offsets. This mode of increase applies specially to bulbous plants, such as the lily and hyacinth, which produce little bulbs on the exterior round their base. Most bulbs do so naturally to a limited but variable extent; when more rapid increase is wanted the heart is destroyed, and this induces the formation of a larger number of offsets. The stem bulbs of lilies are similar in character to the offsets from the parent bulb. The same mode of increase occurs in the gladiolus and crocus, but their bulb-like permanent parts are called conns, not bulbs. After they have ripened in connexion with the parent bulb, the offsets are taken off, stored in appropriate places, and at the proper season planted out in nursery beds. (3) By Tubers. The tuber is a fleshy underground stem, furnished with eyes which are either visible, as in the potato and in some familiar kinds of Tropcc-olum (T. tubcrosum) and of Oxalis (0. crenata), or latent, as in the Chinese yam (Dioscorca Batatas}. For a fuller description see BOTANY, vol. iv. p. 98. When used for propagation, the tubers are cut up into what are called &quot; sets,&quot; every portion having an eye attached being capable of forming an independent plant. The cut portions of bulky sets should be suffered to lie a short time before being planted, in order to dry the surface and prevent rotting ; this should not, however, be done with such tropical subjects as caladiums, the tubers of which are often cut up into very small fragments for propagation, and of course require to be manipulated in a properly heated propagating pit. No eyes are visible in the Chinese yam, but slices of the long club-shaped tubers will push out young shoots and form inde pendent plants, if planted with ordinary care. Division. (4) B&amp;gt;j Division. Division, or partition, is usually resorted to in the case of tufted growing plants, chiefly perennial herbs ; they may be evergreen, as chamomile or thrift, or when dormant may consist only of underground crowns, as larkspur or lily-of-.the- valley ; but in either case the old tufted plant being dug up may be divided into separate pieces, each furnished with roots, and, when replanted, generally starting on its own account without much check. Snffruticose plants and even small shrubs may be propagated in this way, by first planting them deeper than they are ordinarily grown, and then after the lapse of a year, which time they require to get rooted, taking them up again and dividing them into parts or separate plants. Box-edging and southernwood are examples. The same ends may sometimes be effected by merely working fine soil in amongst the base of the stems, and giving them time to throw out roots before parting them. Suckers. (5) By Suckers. Root suckers are young shoots from the roots of plants, chiefly woody plants, as may often be seen in the case of the elm and the plum. The shoots when used for propagation must be transplanted with all the roots attached to them, care being taken not to injure the parent plant. If they spring from a thick root it is not to be wantonly severed, but the soil should be removed and the sucker taken off by cutting away a clean slice of the root, which will then heal and sustain no harm. Stem suckers are such as proceed from the base of the stem, as is often seen in the case of the currant and lilac. They should be removed - CJ FIG. 51. Suckering Iron. in any case ; when required for propagation they should be taken with all the roots attached to them, and they should be as thoroughly disbudded below ground as possible, or they are liable to continue the habit of suckering. In this case, too, the soil should be carefully opened and the shoots removed with a suckering iron, a sharp concave implement with long iron handle (fig. 51). When the number of roots is limited, the tops should be shortened, and some care in watering and mulching should be bestowed on the plant if it is of value. (6) By Runners. A definition of runners will be found in BOTANY, vol. iv. p. 97. The young string-like shoots produced by the strawberry are a well-known example of them. The pro cess of rooting these runners should be facilitated by fixing them close down to the soil, which is done by small wooden hooked pegs or by stones ; hair-pins, short lengths of bent wire, &c. , may also be used. After the roots are formed, the strings are cut through, and the runners become independent plants. (7) By Proliferous Buds. Not unlike the runner, though grow- Prolifi ing in a very different way, are the bud-plants formed on the fronds ousbu of several kinds of ferns belonging to the genera Asplenium, Woodwardia, Polystichum, Lastrca, Adiantum, Cystopteris, &c. In some of these (Adiantum caudatum, Polystichum lepidocaulon) the rachis of the frond is lengthened out much like the string of the strawberry runner, and bears a plant at its apex. In others (Polystichum angular e proUfcrum), the stipes below and the radii-? amongst the pinnae develop buds, which are often numerous and crowded. In others again (Woodwardia orientnlis, Asplenium bulbiferum), buds are numerously produced on the upper surface of the fronds. These will develop on the plant if allowed to remain. For propagation the bulbiferous portion is pegged down on the surface of a pot of suitable soil ; if kept close in a moist atmosphere, the little buds will soon strike root and form independent plants. In the Cystoptcris the buds are deciduous, falling off as the fronds acquire maturity, but, if collected and pressed into the surface of a pot of soil and kept close, they will grow up into young plants the following season. (8) By Layers. Layering consists in preparing the branch of a Layei plant while still attached to the parent, bending it so that the part operated on is brought under ground, and then fixing it there by means of a forked peg. Some plants root so freely that they need only pegging down ; but in most cases the arrest of the returning sap to form a callus, and ultimately young roots, must be brought about artificially, either by twisting the branch, by split ting it, by girding it closely with wire, by taking off a ring of bark, or by &quot;tonguing.&quot; In tonguing the leaves are cut off the portion which has to be brought under ground, and a tongue or slit is then cut from below upwards close beyond a joint, of such length that, when the cut part of the layer is pegged an inch or two (or in larger woody subjects 3 or 4 inches) below the surface, the elevation of the point of the shoot to an upright position may FIG. 52. Propagation by Layers a, tonguing ; b, ringing. open the incision, and thus set it free, so that it may be surrounded by earth to induce it to form roots. The whole branch, except a few buds at the extremity, is covered with soil. The best seasons for these operations are early spring and midsummer, that is, before the sap begins to flow, and after the first flush of growth has passed off. One whole summer, sometimes two, must elapse before the layers will be fully rooted in the case of woody plants ; but suph plants as carnations and picotees, which are usually propa gated in this way, in favourable seasons take only a few weeks to root, as they are layered towards the end of the bl&amp;lt; oming season in July, and are taken off and planted separately early in the autumn. Fig. 52 shows a woody plant with one layer prepared by tonguing and another by ringing. In general, each shoot makes one layer, but in plants like the Wistaria or Clematis, which make long shoots, what is called serpentine layering may be adopted ; that is, the shoot is taken alternately below and above the surface, as frequently as its length permits. There must, however, be a joint at the underground part where it is to be tongued and pegged, and at least one .sound bud in each exposed part, from which a shoot may be developed to form the top of the young plant. (9) By Circumposition. When a plant is too high or its habit Circi] does not conveniently admit of its being layered, it may often be posit increased by what is called circumposition, the soil being carried up to the branch operated on. The branch is to be prepared by ringing or notching or wiring as in layering, and a temporary stand made to support the vessel which is to contain the soil. The vessel may be a flower-pot sawn in two, so that the halves may be bound together when used, or it may be a flower-pot or box with a side slit which will admit the shoot ; this vessel is to be