No corporation shall be authorized to conduct the business of buying and selling real estate or be permitted to hold or own real estate except such as may be reasonably necessary to enable it to carry out the purposes for which it was created, and every corporation authorized after May 1, 1900, to engage in agriculture shall by its charter be restricted to the ownership and control of not to exceed five hundred acres of land; and this provision shall be held to prevent any member of a corporation engaged in agriculture from being in any wise interested in any other corporation engaged in agriculture. Corporations, however, may loan funds upon real estate security, and purchase real estate when necessary for the collection of loans, but they shall dispose of real estate so obtained within five years after receiving the title. Corporations not organized in Puerto Rico, and doing business therein, shall be bound by the provisions of this section so far as they are applicable.