In my former letter on flowers in windows, I omitted one or two things which may be useful knowledge to some of your readers. In such a situation they are peculiarly liable, especially in dry and hot seasons, to be infested with green -fly (Aphis). And there are few things about which I am more frequently asked than the best method of keeping clear of them. Probably no care will prevent these insects appearing at times, though whatever tends to keep the plants healthy and strong, tends at the same time to prevent the ravages of fly; for they are most troublesome, in general, upon a weak plant, or upon one drawn up by close packing, want of light, or superabundant water, and of which the leaves are long-stemmed, and of a pale sickly green, - a condition of things very common with us window-gardeners, and very necessary to be quickly attended to, as the fly is sure to attack such, and increase the evil. Cuttings that are long in rooting themselves are sometimes prevented by them from striking at all; the whole of the sap manufactured by the feeble powers of the nascent plant being extracted. Now, there are many persons who possess the means of employing the usual remedy - tobacco-smoke, but are not aware of its efficacy, or how to apply it.

Such as have a cucumber-frame, or any other box large and deep enough to place over their whole collection, should, when fly appears, except it be in frost, set them out of doors under such a covering; and on a brick therein lay a red-hot cinder or two, and on them a quarter of an ounce of tobacco, not too close to the plants for the hot smoke to burn them, and cover all up close for a quarter of an hour or twenty minutes. On removing the covering, every fly will be found to have perished.

There is, however, another very effectual way, and which, in a collection not exceeding a score of plants, will not occupy more time or labour than the foregoing. Take up each plant separately, and either with the breath, or, if you are afraid of your lungs, with a bellows, blow them off. It will require a brisk puff, for they cling most tenaciously; only let no one who suffers them to remain expect a crop of flowers.

But now respecting the remedy for these drawn-up and pallid weakly plants. My friend Mrs. Wilkins, when she sees any symptoms of this, puts hers out of doors for a time; and her neighbours, seeing how well this answers its purpose, follow her example, and theirs all die, and they wonder how it is they are so unlucky. The fact is, they think the mere doing it will ensure success. While one forgets them, and leaves them out for the night, and a slight morning frost ends the matter; another places them out when there is wind, even an east wind; a third exposes them to the sun: all these errors must be avoided, and, when they are, the plan will generally succeed. I have now (Dec. 13) a large plant in training for a Christmas bloom, which a fortnight ago shewed nothing green about the leaves except the ribs; but now, by exposure to the free open air out of doors, presents the appearance it usually would in April.

But there is another way which, until tried, would be supposed to produce the very opposite effect, namely, to plunge them in a hotbed for a few days. When a plant, spindling and weakening itself, is subjected to bottom-heat, the effect is astonishing. The growth upwards is immediately checked. The branches swell, instead of lengthening themselves, the leaves recover a deep and healthy green; and not till these effects are produced does the upward growth recommence, when they should be removed again.

One of the most common mistakes by which pale leaves are produced is by stimulating applications, by liquid manure, or placing a coating of manure on the top of the pot. The effect of this is not dissimilar to that of giving gin to a child. The minute and tender rootlets cannot bear the strong excitement. They perish, and the plant soon after follows their example, if the pernicious system be persevered in. Eschew all impatient desire of stimulants. Give entirely fresh mould once a year, and let that, if possible, be maiden, and, if you please, pot off into smaller pots for the winter, as I do, to save room; only remembering to re-pot into larger ones in the spring, without breaking the ball of earth. Be sure also to remember the drainage, to prevent the soil becoming sodden and sour - not a mere piece of oyster-shell over the hole, but a handful of broken pieces of pot put in carefully.

One word more about training. One who recommends such a thing must expect to hear a good deal of well-meant nonsense about suffering the plant to grow as nature meant it to grow. Nature never meant any thing. But the Author of Nature has imposed training and discipline as a duty; nor is any person or thing ever brought to the highest perfection it is capable of without restraint, and pruning, and direction, from a fostering hand. Not an apple-tree or a currant-bush will long repay the use of the land they grow on, if their owner forgets the duty incumbent on him in virtue of his descent from Adam, on whom the sentence was pronounced. Thorns, and thistles, and barrenness will soon be found in all things to be the point to which, if left to themselves and to their nature, they will tend. Cultivation is necessary, in order to exhibit the good of which every sublunary nature is capable. Never speak slightingly of training, even in a Geranium. It may teach you a lesson respecting yourself, and the persons committed to your care by the providence of God; and it will amply repay you for your trouble in its floral results. Persons who have never seen a trained plant are incredulous of its effects.

The gardener of a country gentleman in this neighbourhood who had three conservatories under his care, would not believe, on my testimony, that a single stem could be made to support from eight to sixteen or twenty flowering branches, arising from nearly the same height above the pot; but endeavoured to persuade me that it must be done by cheating, and putting many plants into one pot. The method, however, is very easily practised, and is well worth any person's employing on at least a few of his most striking and useful sorts. The principle is this, that no more branches can thrive than can be supplied with a free circulation of air, so as not to interfere with each other. And the mode by which this is insured is equally useful in keeping the origin of the branches low, so as to make a compact bushy plant. And it is so simple, that you may do it, Mrs. Wil-kins, as well as Mr. Dobson himself. If you have a nice young healthy and stocky plant to operate upon, it is better, but not absolutely necessary.

If you have, pinch off its head; and when it breaks out at the sides, either peg down the side-branches as nearly straight out as you can without tearing the joint, or tie them down, which must be done thus: tie a string tightly round the pot, just under the rim; and under this pass a loop of thick worsted over the end of each branch, to keep it down in the position you wish it to grow in.

When the branches reach out as far as you wish them, a little beyond the rim of the pot you mean the plant to flower in, pinch off their ends, and, after they have pushed out their eyes into branches, you may remove the strings, and you have thenceforward a trained plant, to last you many years, and each year better than the last; which only needs cutting down in summer after flowering, and ordinary care afterwards, to be a perpetual beauty in the blooming season. I have now an old Sir Robert Peel with thirteen such branches springing from its rough wooden arms, and plenty of elbow-room for each; which, at eight blossoms to each, will give a total of above a hundred blossoms; and I expect nearly as many from my Aurora, which some say is the handsomest Geranium grown. Moreover, if you do not care about the cuttings, you may, by setting it out in the open air after it has flowered, and protecting it from wind and sun for the first day or two, and bringing it in again when sufficiently hardened, have it flower again, and often as well as at first.

And now, in conclusion, let me recommend every cottager's wife to have a plant or two in her window, but not in the bedroom. The very trouble they give, and it is but a little, is beneficial, for it exercises attention. The care they require tends to produce neatness in other things; and the pleasure with which they repay the care that is given them is a refined, a domestic, and an inexpensive pleasure, and is a means of elevating the tastes and of rendering home attractive. Iota.