In the opinion of Mr Knight and or other emi nent cultivators, the employment of a bark-bed, or bottom heat of any kind, is wholly unnecessary af. ter the crowns or suckers have pushed their roots. In an ordinary hot-house, the pots may be placed en loose piers of brick, and thus raised near to the glass ; a layer of bricks being removed as the plants increase in height. In the summer season, the. temperature may depend chiefly on confined solar heat, qo air being given till the temperature ex ceed 95° Fahr. For soil Mr Knight prefers thin green turf chopped small, and pressed close into the pots while damp ; a piece of whole turf, with the sward downmost, being laid at the bottom of the pots. The surface, however, is covered with vegetable mould and sandy loam mixed. Mr Knight recommends applying daily to the pots, during the height summer, water in which pigeons' dung has been steeped till the colour be nearly as dark as that of porter. A little pure water may be sprinkled over the plants, but this is not to be repeated till all remains of the former sprinkling have disappeared. As the day gets shorter, less of the pigeons' dung water is given, the plants being then less able to feed on it. During winter the house is kept as nearly as possible at 50° Fahr. Mr Knight prefers pots which are little more than a foot in diameter, and he does not seem to consider repotting as necessary: at least, he regards the shifting from smaller to larger pots as detrimental, the matter which would go to the formation of blossom and fruit being thus divert ed to the production of new roots.
It may here be remarked, that for communicat ing heat to pits or frames, it has been found advan tageous, in place of stable litter, to employ the cleanings of a flax-dresser's mill, known under the name of Lint-shows or Flax-pob. This substance ferments very slowly, and the heat is therefore kept up for several months in succession, and very nearly of an equal temperature.
Various improvements and changes in the form and interior arrangements of glazed houses intend ed for the production of peaches, nectarines, figs, and grapes, have of late been introduced or recom mended. These are detailed chiefly in the Transac tions of the Horticultural Society of London, and in the Memoirs of the Caledonian Horticultural Society. Mr Knight and Mr Gowen, with Mr Loudon at Bayswater near London, seem to be the principal persons who have attended to these subjects in England; and Mr Hay of Edinburgh, Mr Beattie at Scoon, and Mr Henderson at Brechin, have led the way in Scotland. Among amateur horticultu rists, our countryman Sir George Mackenzie has distinguished himself by projecting spherical hot houses ; and modifications of this form have been strongly recommended by Mr London.
A very considerable improvement in the mode of glazing hothouses may deserve to be more particu larly mentioned, because it tends materially to obvi ate breakage,. which, on account of the high duty on glass in this country, is now an important object. It
.consists chiefly, in making the upper and lower edges of the panes segments of a circle, instead of being rectilinear or. horizontal ; the upper edge being made concave,,the lower convex. For a pane eight inches wide, .a curvature iths of an inch deep in the centre is sufficient. The advantages of this circular form must be evident. The rain which falls, or moisture which collects on the exterior of the glass, gravitates to the centre of the pane, and runs down in a con tinued line, instead of passing along the sides of the bars, and being partly detained by the capillary at traction of the two surfaces, at the overlapping of the panes. The extent to which one pane overlaps another can, at the same time, therefore, be much • lessened ; and *th of an inch is found sufficient. This narrowness of the lap, again, prevents breakage from the lodging of moisture, and thesudden expan sion produced by freezing during wea ther of winter. When these circular panes are cut from whole sheets of glass, the expence is scarcely greater than- for oblong squares. It is proper that the glass should be very flat or equal ; and the kind knows by the name of Patent Crown Glass should be preferred. In atdves or hot-houses where a high temperature must be maintained, the laps are puttied. In this tse, a Wall central openin& is left in the petty, by inserting a slip of wood at first, and with drawing it when the patio is pressed down to its , bearing ; by this little aperture the condensed va pour generated within escapes without dropping on the plants. The ingenious Mr Loudon uses very thin sheet lead in place of putty, for closing the laps ; he thus avoids all risk of expansion from frost, and the lap can thus be made exceedingly narrow.
Heating of Hot-honsesby Steam.
Of all recent improvements, however, in this branch of gardening, the most important is the use of steam for communicating the artificial heat, in place of depending, as formerly, on the passage of smoke and heated air through flues, aided in particu lar houses, called Stoves, by the slight fermentation of tanners' bark. The principal advantage arising from the use of steam consists in this, that an equable high temperature can thus be maintained for a length of time with much greater ease and certainty. Be sides, in steam hothouses, the plants can scarcely ever be liable to suffer a scorching heat ; the air continues pure and untainted, and persona visiting the house are much less apt to be annoyed with the smell of smoke or soot. In districts where coals are scarce and high priced, the saving of fuel is an ob ject ; and it has been found that seven bushels of coal go as far in keeping up steam heat, as ten bush els do in maintaining an equal temperature the other way. Further, it is evident that, by merely opening a valve, the house may, at any time, be most effectu ally steamed, that is, filled with vapour ; and the warm moisture thus applied to every part of the plants is observed to contribute remarkably to their health and vigour.