Hordeum vulgare. A few days before hatching, the packets of eggs were dissected from the leaves, and placed on a strip of moist filter paper, one end extending out of the mouth of a phial and the other end submerged in water. The bottom of the phial was embedded in soil in a 6-inch flower pot in contact with barley plants. The nymphs upon hatching crawled on the barley plants, and some completed the nymphal stages, but only a low population of adults was reared. The method of obtaining noninfective blue-green sharpshooters, N eokolla circellata, was similar to that first described by Stahl and Carsner (1918) for the beet leafhopper, and later illustrated by Severin (1921). Other species of leafhoppers collected in the field were transferred in lots of 20 adults to healthy grapevines or alfalfa plants, to test natural infectivity before using them in vector-efficiency tests in virus transmission. The vines and alfalfa plants served as control plants. The insects were rarely naturally infective. This confirms the results of Hewitt, Houston, Frazier, and Freitag (1946) with Carneocephala fulgida and H elochara delta. The grapevines used were the varieties Emperor, Ribier, Palomino, and Thompson Seedless (Vitis vin•ifera) propagated from indexed cuttings, and wild grapevine (V. californica) grown from seeds. Vines grown from cuttings were used in all tests with multiple lots and also in all single-lot tests except in 1943 and 1944, when seedlings were used. The alfalfa was in all cases the California Common variety of Medicago sativa. Details of methods used for specific aspects of transmission tests are given in appropriate sections.