Section 19. No person shall sell, exchange, give, deliver or ship within the commonwealth any tree, shrub or plant commonly known as nursery stock unless such person holds a grower’s certificate under section seventeen or an agent’s license under the preceding section, and unless a copy of such certificate or license, or such other evidence as the department prescribes, shall accompany each car, box, bundle or package sold, exchanged, given, delivered or shipped, and unless such certificate or license is dated within twelve months of the date of such delivery or shipment; but this section shall not prohibit the selling, giving or exchanging of trees, plants or shrubs by any person who is not a grower of, dealer in, or agent for nursery stock.