The success of reinforced ply-wood construction in the design of large ribs suggested its application to the construction of large spars such as are used in internally braced construction with thick wing sections. The following development work was conducted to determine the adaptability of reinforced ply-wood web construction to spars, and also to compare the relative merits of the solid-web and trussed-web types. Two series of designs and tests were made on each type of construction. The first test emphasized the necessity of certain design features and the necessity of securing good gluing. The second series of designs incorporated the results of our experience with the first series of designs and is thought to provide an excellent basis of comparison between the solid-web and trussed-web construction.