209. Very commonly the roof is formed of sast:es, which can be let down liar the admission of air. In a grape. house described by Mr Knight. (Hort, Trans. Loud. vol. i. p. 100,) the air is admitted at the ends, where all the sashes are made to slide ; a free current may thus be made to pass !brought the house. Besides, about fuur feet of the upper end of every third light of the roof is made to lift up, being attached by hinges to the wood-work on the top of the back wall ; and in this way, air is given in hot and calm weather, without any additional shade. Here it may be remarked, with great submission to that eminent hor• ticulturist, that currents of air are seldom wanted in hot houses ; they often indeed prove hurtful. To give air, therefore, principally by means of currents seems not a good plan ; for the small openings in the roof are not likely to be able to counteract the rush of cold air at the ends. In giving air to vines, it is of great importance to have a free and soft circulation : this will prove highly salubrious to the plants, while, in the same temperature of the atmo sphere, a current would be hurtful.
210. In planting a new grape-house, the young vines are put in in February or March, and little or no fire-heat is given ; they make strong shoots the first year, but only such as are wanted for trellis are preserved, per haps three on each plant, and in general these are trained straight to wards tile roof, ten or twelve inches separate from each other. In September, if the wood be nut properly ripen ed, a little fire-neat is given fur this put pose. Next year a good deal of fruit begins to appear ; but only a few bunches are permitted to come forward, in order to prove the kinds. In the third year, if well managed, they fill the oar and if the wood be thoroughly ripened, they may be considered as established plants.
211. We shall here mention an incomparably more speedy mode of storing a new grape-house, which may he at.lupt ed wherever a vinery previously exists in the garden, or where there is a friend's vinery in the neighbourhood. This mode is frequently practised at the gardens of Dalkeith House, by Mr James Macdonald, and we have witnessed its complete success.
In the end of June or beginning of July, when the vines have ma& new shoots from ten to twelve feet long, and about the time of the fruit setting, he selects any supernu merary shoots, and, loosening them from the trellis, bends them down so as to make them form a double or flexure in a pot filled with earth, generally a mixture of loam and vegetable mould; taking care to make a portion of last yew's wood containing a joint, pass into the soil in the pot. The earth is kept in a wet state; and at the same time a moist warm air is maintained in the house. In about a week or ten days, roots are found to have proceeded plen tifully from the joint of last year's wood, and these may be seen by merely stirring the surface of the earth, or some times they may be observed penetrating to its surface. The
layer may now be safely detached. Very frequently it con tains one or two bunches of grapes, which continue to grow and come to perfection. A layer cut off in the be ginning of July generally attains, by the end of October, the length of fifteen or twenty feet. A new grape-house, therefore, might in this way be as completely furnished with plants in three months, as by the usual method, above described, in three years. Supposing the layers to be made on the 1st of July, they might be cut, and removed to the new house on the 9th : by the 9th of October, the roof would be completely covered with shoots, and next season the house would yield a full crop of grapes. It is not meant that they should be allowed to do so, if permanently bearing plants be wished for : on the contrary, they should be suffered to carry only a very moderate crop, as it is pretty evident that the roots could not sustain the demand of a full one ; or at any rate, that the plants would necessa rily spew their exhausted state, by barrenness in the follow ing season. By this means the more delicate kinds, as the frontignac, may be quickly propagated : we have seen layers of the Gibraltar or red Hamburgh, made in the be ginning of July, reach the length of thirteen feet before the end of the month, yielding at the same time two or three bunches of grapes. The more hardy, such as the white muscadine, form still stronger plants in that space of time. Little difficulty is experienced in removing the plants from the pots into the holes prepared for them : if there be fears of preserving a ball of earth to the new roots, the pots may be sunk with them, and then broken and removed ; or the plants may be kept in the pots till autumn, when they may very easily be taken out of them without detriment. INIr Macdonald's experience does not lead him to think that plants propagated in this way are less durable than those procured by slower means, and where the roots and branch es bear a relative proportion to each other. But suppos ing they were found to be less durable, it is evident that one may thus very easily keep grape-houses constantly stored with healthy fruit-bearing plants, and that the kinds may be changed almost at pleasure. When it happens that too much bearing wood has been trained in, the plants are relieved, and sufficient sun and air admitted, by thus removing two or three shoots ; and supposing these to contain each several bunches of some fine sort of grape, they are not lost, but may be ripened, by setting the pots on the side-shelves, or flue trellis, of the pinery, or any hot house.