When doctors at the Solace Health Network of cannabis clinics prescribe their patients medical marijuana, one government-licensed producer of the drug might come quickly to mind. The clinics’ parent company, after all, is Terrascend, which also owns a cannabis grower and seller. A direct ownership link between doctor-staffed clinics and the manufacturer of their main treatment tool would be unheard of if it involved a pharmaceutical firm. But in the fast-evolving cannabis industry, Terrascend’s arrangement is far from unique — and quite legal. Close to a dozen companies across the country have combined pot-producing operations and marijuana-treatment clinics under the same corporate umbrella, in what seems to be a growing trend.