A person who directly or indirectly controls a person liable under this act, a partner in a firm so liable, a principal executive officer or director of a corporation so liable, a person occupying a similar status or performing similar functions, an employee of a person so liable who materially aids in the act or transaction constituting the violation, is also liable jointly and severally with and to the same extent as the person, unless the other person who is so liable had no knowledge of or reasonable grounds to believe in the existence of the facts by reason of which the liability is alleged to exist.