We learn from the American Farmer that Mr. W. W. Spence, at Bolton, his beautiful place, which is a charming bit of country almost entirely surrounded by city walls, has recently put up probably the most modern and attractive greenhouse in or near the city. President Perot has annexed to his other structures, at his finished seat on the Charles St. Avenue, quite a large fern and orchid house. Mr. Basin has added a third to his two already well-stocked houses. Captain Snow, of Harford, is contemplating an enlarged planthouse to replace his present ones, which do not give room for flourishing palms and other plants of tall stature. Numerous other alterations have recently been completed, or are in progress.