I was a little surprised to find such a noted plant-grower as Mr Hammond recommending in the 'Gardener' for November the utter destruction of plants of Hoya carnosa infested with mealy-bug; and also, in a former paper on the Ixora, advising the use of cold water, applied with force from syringe or water-engine, as a means of exterminating mealy-bug from the plants. Such practices are now quite unnecessary since the discovery of the paraffin-oil cure. Plants infested with mealy-bug may be simply and safely cleansed by the judicious application of paraffin. My own experience in connection with its use has been mainly amongst indoor plants; and in order to divest the plants of the enemy, the course of procedure is as follows : First of all, secure a shallow wooden tray or tub, into which put two gallons of water, then add two wine - glassfuls of paraffin, which thoroughly mix with the syringe; then the liquid is ready to be applied. The operation is generally performed in the house where the plants grow, as this prevents the possibility of the enemy being carried to any other place where it would be likely to come in contact with other plants not affected.

The water and paraffin being well mixed with the smart use of the syringe until the mixture assumes a slightly whitish appearance, the infested plants may then be taken from their positions in turn, one man holding the plant over the tray or tub, while another applies the mixture with the syringe. It is necessary to syringe every alternate syringeful sharply into the tray, to keep the water and oil well mixed, otherwise the cure will be worse than the disease. Plants of Ixoras, Crotons, Gardenias, Eucharis, Stephanotis, Clerodendrons, Hoyas, and others, have been thoroughly divested of the enemy by this means. Dipladenias are more easily damaged by the oil than the foregoing plants which I have mentioned, and I would advise half the quantity of paraffin for them - viz., one wine-glassful to two gallons of water. Dipladenias are also among the worst of stove subjects to cleanse effectively, as dozens of the enemy will lodge securely under the loose bark on the main stems while the deadly operation is being proceeded with. To overcome this difficulty an extra strong dose should be prepared and applied with a sponge - sponging carefully every part of the stem where they would be likely to harbour.

The Poinsettia is also another plant that ought to be treated similarly to the Dipladenia. I have also used this light mixture for Cucumbers with perfect success, syringing them where they stood growing in beds in a Cucumber-house. The dripping of the oil from the plants on to the bed did not seem in any way to injure the roots of the Cucumbers; indeed, to convince any reader of this, I may mention that one large plant of Croton angustifolius was watered at the root with one wine - glassful of oil well mixed in 1 1/2 gallon of water, to exterminate worms, and another plant of Alocasia macrorhiza received a similar dose for the same purpose. The experiment was performed in spring. Both plants did remarkably well the following summer, the Allocasia throwing up prodigious, beautifully variegated leaves : the Croton also grew well, - the dose in no way affecting either the growth or colouring of these plants. Dipping the plants overhead in the liquid is a dangerous practice, and will not be done twice by any experimenter. The plants should only be allowed to remain five minutes after syringing them with the oil and water, after which they should undergo a thorough drenching with clean water sharply applied by the syringe.

After the operation is completed, it will be necessary to keep the top ventilators of the house open to allow the oily vapour to escape, as the oil evaporating from the floor and other places where it has been spilt during the operation can in no way be conducive to the health of the plants.

If the affected plants in any house are carefully treated in this way three or four times during the winter season, when they are at rest and young growing shoots few in number, little trouble will be experienced with the enemy the following season.

There are doubtless other correspondents of wider experience in the use of paraffin-oil as an insecticide, and the results of their experience would be gladly hailed by many who are as yet unacquainted with its use. A. Dewar.