Section 18. At the trial of any issue of fact in a probate court the presiding judge may appoint a stenographer, who shall be sworn and shall attend the trial, or such part thereof as the judge may direct, and perform like duties and receive the same compensation therefor as a stenographer appointed by the superior court who is not on salary; and the sums so payable for his attendance at court and for any transcript of his notes or part thereof furnished to the judge by his direction shall be paid by the commonwealth upon the certificate of the judge. The judges of probate of any county may appoint a stenographer for the probate court of such county. The compensation and expenses of such stenographer shall be paid by the commonwealth.