Before an appropriation for any purpose to any department, board, bureau, commission, agency, office or institution of the state shall become available, there shall be submitted to the Department of Finance, not less than 20 days before the expiration of the last period for which an allotment has been or shall have been made, a requisition for an allotment of the amount estimated to be necessary to carry on its work during the period for which allotments are made. Allotments shall be made for such length of time as may be determined to be appropriate and convenient by the Department of Finance, with the approval of the Governor, but no allotment (except for the acquisition of land, permanent improvements or other capital projects) shall, in any event, be for a period of longer than three months. Such requisition for an allotment shall contain such information and data and be in such details as may be required by the Department of Finance. The Department of Finance shall examine such requisition and, with the approval of the Governor, shall make such allotment, or modification thereof, as may be deemed necessary, but the total amount of annual appropriations to any department, board, bureau, commission, agency, office or institution of the state shall not be reduced except proportionately as provided for in Section 41-4-90. The Department of Finance shall submit copies of each allotment thus approved to the head of the department, board, bureau, commission, agency, office or institution of the state for which such allotment shall have been made. The Comptroller in the Department of Finance shall set up such allotment on his book and be governed accordingly in his control of expenditures. Allotments of appropriations made for the acquisition of land, permanent improvements and other capital projects may, however, be allotted in one amount by major classes or projects for which they are expendable without regard to allotment periods. Any allotments may be subsequently modified by the Department of Finance, with the approval of the Governor, either upon the written request of the head of the department, board, bureau, commission, agency, office or institution of the state concerned or upon the initiative of the Department of Finance or the Governor, and notice of such modification shall be given and such modification shall be set upon the books of said Comptroller in the same way as in the case of original allotments.