(1) The income of that portion of such fund received from the sale of lots designated as perpetual care lots shall be used, in the discretion of the trustees of such public cemetery district, solely for the care, maintenance, and improvement of such cemetery lots and its grounds, roads, walks, and avenues leading thereto, except as herein provided. The income from such portion of such funds as shall have been paid in by lot owners for the care of specific lots shall be segregated from the other portion, each lot being credited with its respective income, and shall be used solely for the care of such lots, respectively.
(2) In the event of any portion of the income so paid ever remaining unexpended for such purposes for 1 year after its being so paid over to the treasurer of such public cemetery district, it shall be returned to the trustees of such fund by said treasurer and become a part of the principal.