The State Commission of Forestry may borrow from time to time sums of money not exceeding five hundred thousand dollars from any source available and issue evidences of indebtedness therefor in the form of notes or bonds, as may be determined by the Commission, at a rate of interest not exceeding six per cent per annum, payable either annually or semiannually, as the Commission may determine, and with such maturities as may be determined by the Commission, not exceeding, however, twenty years from the date of issue of the first obligation issued hereunder. The Commission may secure any sums borrowed under the terms hereof by mortgage of any property owned by it and it may also pledge any and all income of every kind and pledge any and all rents, incomes, issues and profits accruing to it from any of its properties and any rights or privileges accruing to it under any contract of sale or lease. Unless otherwise provided herein, all of the details of any loan and the manner of execution of the evidences of indebtedness and of the mortgages or other security authorized to be pledged shall be within the discretion of the Commission.