Section 34. The trustees of the Bristol county agricultural school may, with the approval of the commissioner, permit pupils with limited educational preparation to enter for a special course in horticulture, fruit growing or dairy farming. Said trustees may from time to time provide instruction in such of the types of vocational education described in sections one to twenty-two, inclusive, as they may deem advisable and as the commissioner may approve, in addition to the instruction authorized herein and in sections thirty-five, thirty-six and thirty-seven.