§ 19. Planting trees and shrubs along state highways. The commissioner of transportation, in his discretion, may plant rows or groups of suitable trees along the bounds of existing state highways at such places as he may determine and may also plant on the banks of such cuts and fills as were made in constructing, reconstructing or improving such highways such shrubs as are necessary and suitable to prevent or stay erosion thereof. Upon the construction, reconstruction or improvement of any state highway the commissioner of transportation shall plant along such highways rows or groups of suitable trees, except where such highways pass through wooded sections of country, and shall also plant on the banks of such cuts and fills as are made in constructing, reconstructing or improving such highways such shrubs as are necessary and suitable to prevent or stay erosion thereof. The commissioner of transportation may, with the consent of the owner of the abutting premises, enter upon such premises to plant suitable trees or shrubs as he may determine as desirable for reasons of safety and to maintain such trees and shrubs for a period not to exceed two years. The commissioner of transportation is not required to plant shrubs and trees under the provisions of this section should such plantings already be in existence, should the soil in any place be too stony for such planting or should such planting imperil the safety of the public. The work may be done by forces in the department or by contract let to the lowest responsible bidder after due advertisement. Moneys appropriated for the construction and maintenance of state highways shall be available for any of the work authorized by this section.