Physalis mollis is commonly known as smooth groundcherry. Thomas A. Nuttall described it in 1834. It grows throughout Oklahoma. Before the development of prepared fly sprays, the fresh plant was used to control house flies. The bruised leaves and stems, mixed with a little water and sugar, killed flies. L. E. Harris of Ohio State University isolated a glycoside in an impure form; it was toxic to flies. He also isolated an alkaloid, but it was not toxic to flies in the small dosage used.

Nicotiana glauca, tree tobacco, is a wild, fast-growing plant in Texas, Arizona, and California. Patrick J. Hannan and I were granted patents covering two methods useful in extracting the alkaloids from Nicotiana species, including the alkaloid anabasine from Nicotiana alauca. Anabasine is a liquid alkaloid that closely resembles nicotine in its physical, chemical, toxicological, and insecticidal properties. It has been reported to be four or five times as toxic as nicotine to certain aphids of economic importance.

Nicotiana spp. Tobacco and its chief alkaloid, nicotine, have been used since 1690 as insecticides. Nicotine forms salts with acids and most of the nicotine used for insecticidal purposes in the United States is in the form of the sulfate. More than 29 species of Nicotiana have been analyzed for their alkaloid content. Some American tobaccos used in making cigars of low nicotine content contain as much as 0.7 percent of nornicotine. One-eighth of the total alkaloids in certain samples of commercial nicotine sulfate solutions was nornicotine. Most species of aphids may be controlled with concentrations of 1 part nicotine to 1,000 parts of water. Nicotine is recommended against only those insects that have soft bodies and those that are minute in size, such as aphids, whiteflies, leafhoppers, psyllids, thrips, spider mites, and some external parasites on animals.

Stemonaceae. Stemona tuberosa, or paipu, has long been known and used in China as an insecticide. Decoctions of the dried roots are said to be toxic to crickets, weevils, and the caterpillars of moths and butterflies. A 50-percent alcoholic extract of the plant is effective against lice and fleas.

Umbelliferae (Carrot Family). Carum carvi is called caraway and contains oil of caraway, which will help cure scaly-leg of poultry. Hartzell and Wilcoxon found that acetone extracts of the seed killed go percent of the mosquito larvae they tested.

Conium maculatum, poison hemlock, contains an alkaloid, confine, which is related to nicotine.

Coriandum sativum, or coriander, contains an oil that repels screw-worms. Applied in a 2-percent oil emulsion spray, it kills spider mites and cotton aphids. Coriander oil repels house flies, green bottle flies (Lucilia sericata), and black blow flies.

Pimpinella anisum is anise. Clothing treated with a soapy emulsion of anise oil protects wearers from the sting of gnats. Anise oil repels black blow flies, house flies, and green bottle flies.

Vitaceae (Grape Family). Parthenocissus quinquefolia, or Virginia creeper. An old reference to it states that a bunch of leaves rubbed on an infested area of an apple tree and crushing all the woolly apple aphids, made the tree entirely free of aphids a week later. Formerly the tree could not be kept free of aphids for any length of time.

THE PLANT WORLD contains many interesting and useful insecticides that have not been investigated yet. Only a few have been mentioned here. The entomologists and chemists have passed by many thousands of plants in their search for an insecticide that kills insects but is safe to people and animals.

Once a scientist discovers a plant useful as an insecticide, he must take the plant apart and discover the active principles in it. The discovery is only the first step toward the commercial usefulness of the plant. The next steps take time and effort.

That a plant is poisonous to other animals or is a common weed rarely attacked by insects is not a positive indication of insecticidal properties. The insecticidal principles may be present in one or more of the following parts : Leaves and leaflets, flowers, petioles, seeds and seed hulls, fruits, twigs and stems, roots, bark, and wood.

Often the plant will be insecticidal when it is ground up, but the extract of the material will not be poisonous.

The farmer and the general public share in the discovery and development of new insecticides from plants. Growing new plants for insecticides means new income to the farmer; the public gets farm products that are clean and free from insects and poisonous residues. Since 1947 Department research on plant insecticides covering only six plants: tree tobacco, oxeye, sabadilla, devils-shoestring, thunder-god vine, and sesame has led to the publication of more than 17 papers and the granting of three public service patents.

Louis FEINSTEIN, a research chemist, joined the Department of Agriculture in 1939. He holds degrees from Georgetown University and the University of Pennsylvania. Dr. Feinstein has published papers on vitamins and nicotine alkaloids and holds patents on the extraction of alkaloids and other materials from plants.