Alvin R. Allison brought this suit in Hockley County, Texas, against L. G. Yarborough, Sr., and L. G. Yarborough, Jr., d.b.a. L. G. Yarborough & Son, residents of Midland County. In Paragraph I of his petition the plaintiff alleged (a) that plaintiff and defendants took oil and gas leases in defendants names on seven tracts of land situated in Hockley County and (b) that the leases were acquired with the understanding that each party was to own a one-third interest in them.