A literature review of rubber-bearing plants in the United States was made, and the essentials of distribution, ecology and rubber content presented in condensed form. Filed lettuce of the specie Lactuca scariola was investigated to determine its place among the other rubber-bearing plants.

Nearly pure stands of natural growing wild lettuce were harvested and the weights of plant material determined. Yields up to 2,830 pounds of dry leaves together with 5,760 pounds of dry stems per acre were obtained. The seasonal variation in rubber content and resins of one natural growing wild lettuce stand was studied from the time of the appearance of flower buds to the end of the growth cycle. At this time of maximum rubber content of this stand the calculated yield was between 1.16 and 1.57 pounds of rubber per acre.

An experimental planting was undertaken to determine rubber content, resin content, and growth and cultivation characteristics of the earlier stages of growth. Young plants gave up to 0.339 percent rubber and a calculated yield of 13.7 pounds of rubber per acre.

Drying temperatures up to the 180°F gave no decreases in rubber content during drying. The rubber content of harvested plants was found to decrease rapidly on exposure to sunlight.

At least 10.7 percent of the seeds were found to have the power of germinating soon after ripening. Seeds ripened in the fall were found to have between 49 and 68 percent germinating power.