green in liquid form should always be accompanied by unslacked lime, as this counteracts the burning effect of Paris green for tobacco spraying. The following formula is recommended:

In preparing this mixture the lime should be slacked in a small amount of hot water, using just enough to keep the lime from burning dry. As soon as the lime is slacked, it should be stirred into the whole amount of water, and the Paris green (which has been previously mixed with just enough water to make a thin paste) is then stirred in. Twenty to 50 gallons of this mixture is usually sufficient to spray an acre of tobacco.

In using Paris green in dry form, it should be mixed with cheap flour, dry air-slacked lime, or other dry, finely powdered substance. These substances do not add anything to the value of the poison, but simply act as carriers to make it possible to apply the mixture more uniformly. The usual formula is

20 to 30 pounds flour or lime.

1 pound of Paris green.

In preparing the dry Paris green mixture, care should be taken to see that the Paris green is thoroughly mixed with the other substance used. The whole mass when thoroughly mixed will be of a uniform light-green color without any streaks or lumps of darker green. From one-half to one pound of pure Paris green will cover an acre of tobacco when used in this way. Paris green in the dry form is applied preferably while the dew is on the plants or just after a rain, as it will stick much better when used in this way.

Kerosene Emulsion.-The use of this spray mixture for Flea Bugs in tobacco seedbeds was not attempted until too late to give it a very thorough test. A heavy drenching spray of this mixture was applied to the remnants of tobacco plants left in the seedbeds and a noticeable reduction in the number of Flea Bugs was noticed. Even with this heavy drenching spray only a very slight burning effect was noticed on the tobacco-so slight, indeed, as to be absolutely disregarded in practice. This spray promised excellent things when used against the Flea Bugs, but inasmuch as our experiments have not been carried far enough to be conclusive, it should be used only in an experimental way, if used at all, and if it proves successful under your conditions, it may be used more extensively the following year.

Kerosene emulsion is usually prepared according to the following formula:

The soap is shaved into a kettle containing the water, which is boiled until the soap dissolves, then remove from the fire and add the kerosene. The mixture is then pumped through the spray pump and nozzle back into itself until it has the appearance of thick milk and no globules of free kerosene can be noticed. This stock solution will keep indefinitely. For use, take 1 gallon of stock and add 6 gallons water.

DANGER FROM THE USE OF ARSENATES ON TOBACCO.

There exists in the minds of many people a strong prejudice against the use of poisons (arsenates) on any plant that is used for a food. Needless to say this same prejudice has to be met when one advises the use of arsenates for tobacco spraying. Of course, caution should be used in this matter. We would not apply any poison to tobacco directly before it is harvested, and some time should always intervene from the time of the last spraying until the tobacco is harvested. Certainly two weeks should be allowed, and three or four would be much better. Then by the time the tobacco is harvested the wind and rains have had a chance to remove all but the last traces of poison. To show clearly that the amount of arsenate used on tobacco is not at all dangerous, it is necessary only to call attention to the following facts: (1) At the rate arsenates are used, not enough could be secured by any one person at any one time to prove injurious. (2) Not all of the spray mixture used reaches the plant. (3) Of the amount that does reach the plant only a very small percentage can remain until the end of the season.

The amount of arsenate used originally is not sufficient to cause alarm. Our experiments show that 4 pounds of arsenate of lead would spray an acre of tobacco. The average sample of arsenate of lead contains from 10 to 20 per cent of arsenous oxide (arsenic), which is the real poison in the arsenate of lead. One and one-half grains of arsenic are said to constitute a fatal dose for an adult. In 4 pounds of arsenate of lead there would be from 2,800 to 5,600 grains of arsenic, depending upon the strength of the arsenate of lead used. Assuming, then, that all of the arsenate used reaches the plant, and that all of it remained upon the leaf until harvest time, there would be left on each acre of tobacco for every spraying made, from 1,860 to 3,730 injurious doses. Assuming that three sprayings are made during the season, there would be at the end of the year 8,400 to 16,800 grains of arsenic on an acre of tobacco, provided all of the spray mixtures used reached the plant and that none of it was washed off or blown away during the season. In other words, there would be approximately 3 grains for each plant. However, as stated below, at least 25 per cent of the original mixture used is wasted, and certainly it seems safe to say that 95 per cent of the amount that

actually reaches the plant would be removed by natural causes in the course of the year. This would leave, then, approximately 700 grains to each acre of tobacco sprayed-about one-seventh of a grain to a plant. Assuming that 4 plants will yield approximately a pound of tobacco, this would mean that there would be approximately onethird of a fatal dose to every pound of tobacco harvested. Since only a very small amount of tobacco is swallowed, in whatever form it is used, it seems safe to say that no one person would at any one time consume enough tobacco, sprayed with arsenates as indicated above, to be injurious.

It seems almost needless to say that not all of the spray mixture used reaches the tobacco plant. This is very evident indeed to any one who has ever done any spraying. It seems safe to say that on still days, under the most favorable conditions, that at least 25 per cent of the spray mixture used is necessarily wasted in this way.

Of the amount of poison that reaches the plant, the greater percentage must be washed away by rain or blown away by the wind. Experiments carried on by Professor Garman, of the Kentucky Experiment Station, prove conclusively by chemical analysis that of the amount of poison that reached the plant originally from 96 to 98 per cent was removed in this way in a month after the plants were sprayed.

These arguments hold true for Paris green as well as arsenate of lead. Assuming that one pound of Paris green is used to an acre of tobacco, and that three sprayings are given throughout the season, we would have 12,600 grains of arsenic used per acre, assuming that Paris green contains 60 per cent of arsenic, which is above the average sample, and discarding the usual 25 per cent for spray mixture wasted in making the application, and 95 per cent of the arsenic which actually reaches the plant, we will have left 3-40 of a grain of arsenic per plant-in other words, a fatal dose for every five pounds of tobacco harvested.

INSECTS IN GENERAL.

In order that the farmer may successfully combat the different insects which injure tobacco, it is necessary to know something regarding insects in general, their life-histories, habits, enemies, and the remedies that may be used against them successfully.

Life-histories. Briefly, insects may be divided into two classes. One develops from the egg to the adult without any resting stage. Insects belonging to this class are said to have an incomplete change of form. The other class has a resting stage in its life-history, and insects belonging to this class are said to have a complete change of form. In incomplete change of form there are three stages in the

life cycle of the insects. First, the egg, which is laid by the adult and from which an active, usually rapid growing "nymph" is hatched. This "nymph" is wingless, and from it, without any intermediate resting stage, the winged adults develop. Grasshoppers may be taken as an illustration of insects of this class. The wingless young are familiar objects to every one. It is this stage of insects with incomplete change of form that are known as "nymphs." (Fig. 7.)

b

FIG. 7.-Life-history of the Grasshopper (all figures enlarged). (a) Egg (redrawn from Riley); (b) nymph (original illustration); (c) adult (original illustration).

Insects belonging to the second class have four stages in their life-history. Eggs laid by the adults develop into larvæ, or worms, as they are commonly known. Horn Worms may be taken as an example of this stage in the development of insects of this class. The larvæ is the active growing period, and is followed by a resting period which is known, technically, as the "pupa" or "chrysalis." this pupa, after a length of time, the adults emerge. (Fig. 8.)

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It is necessary for the farmer to know the details, the life-history, of the insect he is trying to conquer in order that he may fight it intelligently. Many insects are practically uncontrollable except for a very brief period or a short stage in their life-history. These various details of the life-histories of the tobacco pests will be considered under their proper headings.

FIG. 8.-Life-history of Southern Horn Worm. (Same as Frontispiece.) (a) Adult (natural size); (b) egg (enlarged); (c) larva (natural size); (d) pupa (slightly enlarged). (From photographs by the author.)

Groups of Insects. All insects are divided into groups according to their structure. The structure of the mouth parts is of vital importance in arranging insects under their proper groups. The structure of the mouth parts is also of vital importance to the farmer who is attempting to control the insect pests of tobacco. Fundamentally, insects are divided into two classes, one of which is provided with biting mouth parts and chews its food. Insects of this class usually make their presence known by eating large, irregular holes in the leaves, by eating away portions of the roots or by hollowing out the stem. The insects of the second class are provided with piercing mouth parts. Insects of this class secure their food by inserting