Tne following letter and reply have been kindly handed to us by Mr. Peter Henderson :

Pottsvim.e, December 5th, 1884.

"Dear Sir: 1 built four greenhouses last summer and put 2000 ft. of pipe in for heating, that was dipped in gas or coal tar. It is injuring my roses and I would like to have your idea as to how to remedy it without taking out pipe. I am at present changing the water in the pipes which has been in since September. There is a great deal of gas-poison passing out with the water. An early answer will very much oblige, Yours truly, J. M. M".

"J. M. M.," you have been unfortunate in making the same blunder that is made by some florists, again and again each year, in the face of repeated warnings that have been given in the Gardeners' Monthly and other magazines, about the dangers of using coal or gas tar on the iron pipes used for hot water or steam in greenhouses. The changing of the water as you propose will not abate the mischief; nothing whatever will do any good except to take down the pipes and burn every part of them where the gas tar is. They must be heated nearly to a red heat so as to expel the gas, as the tar penetrates right through the grain of the cast iron. If you do not take out the pipes and burn them you will find that your roses will remain leafless as long as you continue to fire - do it at once or you will throw your coal and labor away the entire winter. I receive two or three such letters as yours every year - some of them have tried scraping the iron and have used chemicals with the hope of neutralizing the gas, but all without effect - nothing will expel it but heat.

Peter Henderson.