Not to trespass on your valuable space, I will, as briefly as possible, describe the method of forcing lettuce, as practised by the market gardeners in the vicinity of Jersey City. The dates used, of course, are only applicable to this district and others of similar temperature.

The varieties used are the "Winter" or Brown Dutch, Black-seeded Butter, and Silesia. The seed is sown in cold frames from the 15th to the 25th of September. There is no necessity of pricking out or transplanting lettuce, if the seed is regularly sown on a level surface. On the approach of severe weather - generally about the beginning of December - the young plants are covered by sashes at night, but fully exposed during the day in mild weather, so that by the time they are wanted for planting in the hotbeds they are strong and hardy. We vary the time somewhat in commencing forcing, according to the state of the weather, but our usual time is the first week in January. The first operation is the preparation of the manure, which is fresh from horse-stables, as free from straw as possible; (but in this we have not always a choice;) it is carted into a sheltered spot, and thrown into piles in sufficient quantities to ferment. It is then turned over twice at intervals of four or five days, when it is in the proper condition to put into the forcing-pits.

It is in the structure and use of these pits that our mode of operations differs essentially from the usual practice in private establishments. The pits are from two and a half to three feet deep; the sides are boarded up with spruce plank, which, if painted with coal tar, will last for fifteen or twenty years. The back board is allowed to rise nine or ten inches above the surface, the front board five or six inches; this gives but a slight angle, but that we do not think any disadvantage. The width of the pit is six feet; the most convenient length we find is about sixty feet, sufficient for twenty sashes. The space allowed between the rows of pits for walking is four feet.

The manure when put in is made moderately firm to the depth of eighteen or twenty inches ; it is then covered to the depth of six inches with soil. When the soil indicates a "falling" temperature of 80 degrees, the lettuce is planted at about six inches apart, or about fifty plants in a sash ; with due attention to airing in fine weather, and covering up by straw mats at night, the salad is fit for market in six weeks from the time of planting, usually about the middle of February.' This - the first crop - usually gives a return of about $2 50 per sash.

As soon as the crop is cut out, the soil is thrown off, and about six inches of hot manure is again thoroughly mixed through the now almost cold bed ; this in a day or two again enlivens the whole mass, when the bed is planted over again for the second crop. This is usually sold off by April 1st, and is generally very fine, averaging $3 a sash. The weather by this time is warm, and no further advantage is taken of the hot manure ; but the pits are again planted for the third crop, which comes in about May 1st; this last is rather late, and does not give more than $ 1 50 per sash). The three crops thus give coll6ctivcly $1 per sash.

The advantage we claim for using sunken pits for forcing, over making the hotbed on, or partly on, the surface, is two-fold : First, the saving, of the heating material, as only the width of the sash is required, while by the "three-light frame" system you require to make the bed nearly one foot wider on each side than the sash or frame. Again, by the action of the cold on the exposed hotbed the heat is much sooner exhausted than when in the pit, which is comparatively free from such influence.

It would be somewhat difficult to get at all the items of expense in the matter. The manure is used for the out-door crops, and the labor is performed by hands that are used for other purposes ; but that the operation gives a fair profit, the best evidence is, that it is extended annually at an increase of nearly one-third, without diminution of prices. The growing of lettuce in cold frames is practised by us to a much greater extent, but as it may form the subject for some future communication, I need not further allude to it here.

[Mr. Henderson's experience as one of the most extensive and successful growers in the vicinity of New York gives special importance to his article. Our readers will no doubt be impatient to see his article on cold frames. - Ed].