Towns, ecclesiastical societies and cemetery associations may receive and hold in trust donations, the income of which is to be used wholly or in part for the care or improvement of their cemeteries and burial lots or of private lots within such cemeteries or elsewhere. All such donations shall be invested as by law required for the investment of trust funds, except when otherwise authorized by the donors. The principal of two or more such trust funds may be combined and merged in a single fund for the purpose of the investment of the same.