S. O. K., Jackson, Mich., writes: - "Since noticing your remarks on the display of "Rock-work " on the horticultural grounds at the Centennial, the query with me has been why an untutored eye like mine should have been so much attracted by the striking effect produced. May it not be that the perfect harmony and fitness of the plants used in ornamenting the same, made it somehow befitting in placing it in such strong contrast with its surroundings? The Yuccas, Agaves, Aloes and various plants of this class all seemed in such harmony with the design that I queried whether it all had not a right to be there in that prominent and beautiful spot. I noticed also in some greenhouses in Philadelphia, slate placed upon the benches before the covering of sand. I suppose to protect from decay, etc. I think I have discovered a better plan. I put a liberal sprinkling of broken rosin on the benches, then apply a hot flat-iron, forming a perfect coating, which is quickly done, and it is all right for all time to come, so far as I know."

[Yes, the choice of plants for the Rock-work was admirable. The whole work meritorious. Slate is used not only because of its endurance - but it is a better conductor and plants on it are warmer than on boards.. Ed. G. M.]