A circular of the Manly & Cooper Manufacturing Company, respecting iron greenhouses, leads us to inquire of our readers what has been the experience of any of them of late years. They are in favorable use in some parts of the Old World, but have never become popular here. In old times, when the glass was puttied in, one would readily believe, in our very cold and very hot country, the expansion and contraction of the metal would crack the putty and induce leakage, - but, with the many contrivances for avoiding putty, that might not be an objection now. Possibly the heat would pass away too rapidly in cold weather, through the conducting power of the metal; but if this be an objection, there ought to be the merit of durability to iron. Some years ago the Resor iron conservatory, near Cincinnati, was regarded as a great success. It would be interesting to know if it still exists.