Page:Encyclopædia Britannica, Ninth Edition, v. 12.djvu/258

246 246 abundant, short, and not so vigorous as to rival the lead ing members. The Half-fan mode of training, which is intermediate between horizontal and fan training, is most nearly allied to the former, but the branches leave the stem at an acute angle, a disposition supposed to favour the more equal distribution of the sap. Sometimes, as in fig. 84, two vertical stems are adopted, but there is no particular ad vantage in this, and a single-stemmed tree is more man ageable. The half-fan form is well adapted for such fruits as the plum and the cherry; and, indeed, for fruits of vigorous habit, it seems to combine the advantages of both the foregoing. Trees must be fixed to the walls and buildings against which they are trained by means of nails and shreds, or in cases where it is desired to preserve the wall surface intact, by permanent nails or studs driven in in regular order. Sometimes the walls are furnished with galvanized wires, but this has been objected to as causing cankering of the shoots, for which, however, painting is recommended as a remedy, and which is also avoided, it is said, by crossing the tying material between the wire and the wood, and so preventing them from coming in contact. If they are adopted, the wires should be close to the wall to prevent a cold draught between it and the tree. Care should be taken that the ties or fastenings do not eventually cut FIG. 84. Half-Fan Training. into the bark as the branches swell with increased age. When shreds and nails are used, cast wall nails and &quot; medicated shreds &quot; are the best ; the nails should be of small size for the young shoots. For tying plants to trellises and stakes nothing is better than soft tarred string. Osier ties are sometimes used for espaliers. The training in of summer shoots on wall-trees is often done by means of slender twigs ; indeed the prun- ings of the trees themselves, stripped of their leaves, often serve the purpose very well ; the ends are tucked under the adjacent fixed shoots, the young shoots to be fastened in being thus held close to the wall. Crooked shoots should be straightened at the principal or winter training ; this is done by pulling the convex side towards the straight line desired by means of the tie or shred, the next above and below being set so as to pull in the oppo site direction. In training greenhouse plants the young branches should be drawn outwards by means of ties fastened to a string or wire under the pot-rim ; the centre then fills up, and slender stakes are used as required ; but the fewer these are in number the better. Climbers are trained from the bottom around or across trellises, of which the cylin drical or the balloon-shaped, or sometimes the flat oval or circular, are the best forms. The size should be adapted to the habit of the plant, which should cover the whole by the time flowers are produced. Bast fibre and raphia fibre are to be preferred for light subjects of this character, as they can be split to any degree of fineness ; but the latter is not durable enough or strong enough for coarse- [FOECING. growing border flowers. Very durable trellises for green house climbers are made of slender round iron rods for standards, having a series of hooks on the inner edge, into which rings of similar metal are dropped ; the rings may be graduated so as to form a broad open top, or may be all of the same size, when the trellis will assume the cylindrical form. Fig. 85 shows a pot specimen of clematis trained over a balloon-shaped trellis. FIG. 85. Clematis trained on Balloon-shaped Trellis. The training of bedding plants over the surface of the soil is done by small pegs of birch wood or bracken, by loops of wire, or sometimes by loops of bast having the ends fixed in the soil by the aid of the dibble. The object is to fill up the blank space as quickly and as evenly as possible. 27. Forcing is the accelerating, by special treatment, Fore of the growth of certain plants, which are required to be had in leaf, in flower, or in fruit before their natural season, as, for instance, the leaves of mint at Eastertide or the leafstalks of sea-kale and rhubarb at Christmas, the flowers of summer in the depth of winter, or some of the choicest fruits perfected so much before their normal period as to complete, with the retarded crops of winter, the circle of the seasons. In the management of artificial heat for this purpose, a considerable degree of caution is required. The first stages of forcing should, of course, be very gentle, so that the whole growth of the plants may advance in harmony. A very hot atmosphere would unduly force the tops, while the roots remained partially or wholly inactive ; and a strong bottom heat, if it did not cause injury by its excess, would probably result in abortive growth. Any sudden decrease of warmth would be very prejudi cial to the progress of vegetation through the successive stages of foliation, inflorescence, and fructification. But it is not necessary that one unvarying range of temperature should be kept up at whatever pains or risk. Indeed, in very severe weather it is found better to drop a little from the maximum temperature by fire heat, and the loss so occasioned may be made good by a little extra heat applied when the weather is more genial. Night temperatures also should always be allowed to drop somewhat, the heat being increased again in the morning. In other words, the arti ficial temperature should increase by day and decrease by