Section 18. Such stock corporation may grant options to purchase, issue and sell shares of its capital stock to its directors, officers and employees, or to a trustee on their behalf, without first offering the same to its shareholders, for such consideration, not less than par value, and upon such terms and conditions as shall be approved by its board of directors, by the holders of a majority of the stock entitled to vote with respect thereto and by the commissioner. In the absence of fraud, the sufficiency of consideration as so approved shall be conclusively presumed.