plants can be placed for fumigation. If this is made to contain ten cubic feet, about one dram of the cyanide and one and one-half drams each of the sulphuric acid and water will be required.

For use in a greenhouse, it will be well to wet the glass, so as to close as many of the cracks as possible. Night should be selected, as the action of light and the usual high temperature of the daytime will increase the chance of injury to the plants, and lessen the injury to insects. The plants should be on the dry side, and the air moderately cool. At intervals of from thirty to forty feet, place in the walk a tall two-gallon earthen jar. Thus, for a house one hundred feet long, three jars will be required, unless it is very narrow, or very wide, when the number should be decreased or increased accordingly. In each jar place a proportionate part of the water required for the house, and then carefully add an equal amount of sulphuric acid. Care should be taken not to allow any of the acid to come in contact with the clothing, or person, as it is very acrid and will destroy anything that it touches.

The amount of cyanide of potassium required for each jar should be weighed out and placed in paper bags, and just before it is to be used it should be placed inside another larger bag, to prevent any danger of the bag giving way while preparations are being made. Screw eyes are then fastened in the woodwork directly over each jar, and through these stout cords are run to the end of the house near the door, where they are fastened. To the ends over the jars tie the bags of cyanide, so that, on the ends of the strings at the door being released, they will drop into the jars. When all is ready, close the ventilators, pass to the end of the house and carefully lower the bags into the jars and close the door. If any of the cyanide drops into the acid while in the house, hold the breath and get out of the house as soon

as possible, as to inhale the gas is fatal. After twentyfive minutes, open the houses for at least half an hour, but do not enter even then unless obliged to, except with caution. At the usual price of pure cyanide of potassium, 30 to 35 cents per pound, and of commercial sulphuric acid, which can be bought in quantity at three or four cents per pound, the cost of fumigating a greenhouse will not be more than 12 to 15 cents per 1000 cubic feet. While it is very useful in destroying aphides, it is a particularly valuable remedy against insects and mealy bugs.

One of the first uses to which it was put was the destruction of white-tailed mealy bugs (Orthezia insignis) upon coleus, which had refused to yield to other remedies. Its next extensive use was for the black violet aphis, in the houses of Mr. W. G. Saltford, Poughkeepsie, N. Y. (Fig. 111), the results of which, as reported in The Florist's Exchange, were very satisfactory.

The same remedy is also much used upon nursery stock that has been dug for shipment.

An air-tight shed arranged for ventilation is required. While in a dormant condition the trees will stand a stronger gas than will tender greenhouse plants. One ounce of the cyanide of potassium and one and one-half ounces each of water and sulphuric acid can be used with safety for each one hundred and fifty cubic feet. For the San Jose scale a second treatment will be desirable, but one application will suffice for all other insects. The same care about inhaling the fumes should be used here as in a greenhouse.

CHAPTER XXVI.

DISEASES OF GREENHOUSE PLANTS.

FUNGOUS DISEASES OF THE ROSE.-BLACK SPOT.

(Actinonema rosa, Fr.).

This disease, which is the cause of the black spots that are so commonly seen upon the leaves of moss and hybrid roses in wet seasons, frequently invades the greenhouse and causes the leaves of the tea roses to take on an unhealthy appearance and finally to drop from the stems. Its development here seems to be invited by the same conditions as in the open ground. If the bed is poorly

drained, or has been over-watered, a drop in the temperature below 50 degrees is likely to cause the fungus to appear. The "spot" when first seen is of a dark brown color, with an irregular margin (Fig. 112); it rapidly enlarges and in a short time the portion of the leaf around the spot takes on a sickly yellow color and the leaf drops. A magnified section of the leaf is seen in Fig. 113. The dark bodies (A) are the outer layer of epidermal cells, the contents of which have been changed by the fungus into a dark brown granular substance, which can be seen through the transparent cuticle of the leaf, and gives it a brown or black appearance. The mycelium also penetrates the underlying cells and draws its nourishment from them, thus breaking down the tissues and causing the surrounding por

The

tions of the leaves to take on a brown color. spores of the fungus are developed on the mycelium, just beneath the cuticle, and, as this finally bursts and rolls back, they appear as at B. When magnified 500 diameters, the spores are seen to be two-celled (B) and oblong in shape. If they fall upon a damp rose leaf they will germinate and cause another "spot" to form. For the destruction of this fungus,

a perfect remedy is found in Bor- BAM deaux mixture, except for its giving

the plants a whitewashed appear

ance. The copper carbonate solu- FIG. 113. BLACK SPOT, Section magnified. tion is nearly as effectual and does

not have this fault. Evaporated sulphur will also keep the disease in check. As in most other cases, prevention will be found the best cure, and to effect this have the beds well drained, avoid over-watering and maintain a regular temperature of from 56 to 60 degrees, according to the requirements of the variety.

POWDERY MILDEW OF THE ROSE (Sphærotheca pannosa.)

This common disease of the rose appears as a mealy or powdery covering upon the young leaves, and if the attack is severe they become twisted and distorted, and the disease even affects the stems. It develops rapidly upon the young leaves, its mycelium forming a fine cobweb from which the spore-bearing stalks are sent up. These stalks or hyphae become constricted and break up into oval bodies-the spores, which are so numerous as to form a fine powder upon the leaves, whence the name of the fungus. This disease has another form of reproduction, the spores of which are formed in the fall and are designed to carry the disease through the winter. The spores are in sacs, which are themselves enclosed in thick sac known as a theca. The winter spore cover