But in greenhouses of modern construction, in order to have as much glass as possible in front, the piers between the sashes are commonly of timber only, from six to eight or ten incIrts thick, according to the height, so as to admit as great a put that of light and heat of the sun as possible, and the roofs are w holly of glazed frame-work.
The greenhouses fur large collections of plants have some. times two wings of smaller dimensions, added to the main huildiw, at each end, in a right line, separated sometimes limn it by a glass partition, with sliding far cation, and the flout almost w holly of glass-w (irk, and half or whole glass roofs. Thus, by these additional w ings, the houses consist of three divisions, whereby the different qualities and temperatures of the various plants can be more eligibly suited. The middle, or main division, may he for all the principal and more hardy, woody, or shrubby kinds, which require protection only from frost ; one of the w appro priated for the succulent tribe, and the other to the more tender kinds, that require occasionally heat in w ;tact-. but which can live without the heat of a stove or hot house.
On whatever plans greenhouses are constructed. the whole of the inside walls should be neatly finished off \VIII] plaster and whitewash. and the wood-work painted white; the be e toil! being paved with large square paving tiles, or some similar material.
In the greenhouse there should be stands, frames, 0! tressels, which may be moved in and out, upon which rows of planks may be fixed, so as to place the pots or tubs of plants in regular rows, one above another ; by which their heads may be so situated as not to interfere with each other. The lowest rows of plants next the windows should be placed about four feet from them, that there may he a convenient breadth left to walk in front ; and the rows of plants should rise gradually from the first, in such a manner, that the heads of the second row may be entirely advanced above the first, the stems only being hid ; and at the back of the la alse a space allowed of at least five feet, for the convenieney of watering the plants, and to admit a current of air round them, that the damps occasioned by their perspiration may be the better dissipated ; when this is not done, the damps. pent in tot' closely, often occasion a mouldiness upon the tender shoots and leaves, and, when the house is close shut up. this stagnat ing rancid vapour is often very for which reason the plants should never be crowded too close to each other, nor should succulent plants ever be placed among them.